The Seton estate was then purchased from the British Government by the York Buildings Company who put it up for public sale.  The estates of the last Earl of Wintoun were forfeited to the Crown on his attainder, for the part which he took in the Jacobite rising of 1715. They were vested by Act of Parliament in the King for the public interest, and Commissioners were appointed for inquiring into their condition. Owing to the numerous obstacles thrown in their way, it was not until the autumn of 1719 that the Commissioners were ready to dispose of the forfeited lands. In a number of instances the forfeited estates were bought back for the family of their former proprietors, but none of the Setons appear to have been able to purchase the Wintoun property, as the main line was extinct. On the 6th of October the Wintoun estate was put up for sale by auction, and, with a trifling exception, was purchased by the agent of the York Buildings Company for the sum of £50,300. It appears, from an official survey taken in the years 1716 and 1717, that the rental of the estate amounted at that time to £3,393. Of that sum only £266 7s. 9d. was payable in money; £876 18s. 4d. was payable in wheat valued at 10s. 5d. per boll, £1,019 12s. 2d. in barley, and £166 2s. 6d. in oats, both valued at the same price as the wheat. The salt-pans and coal-pits were reckoned at about £1,000; [The company attempted to work the coal-mines and salt-pans at Tranent. They fitted up one of the new fire engines, the first of the kind in Scotland, and made a wooden railway between one and two miles long, connecting the pits with the salt-works at Preston and the harbour at Port Seton. After an expenditure of £3,500 they could not clear £500 a year from the coal-pits and salt-pans combined. They let them for £1000 a-year to a ‘competent person,’ but in no long time he gave up the lease, because he could not make sufficient to pay the rent. The company also tried glass-making, and set up a manufactory for that article at Port Seton; but, on balancing their accounts at Christmas, 1732, they found that they had lost £4,088 17s. 5d. by the experiment.] 749 capons at 16d. each, and 802 hens at 6 2/3d. each, amounted to £53 10s., and 504 thraves of straw, at 5d. per thrave, to £10 10s. 

 The York Buildings Company ultimately became bankrupt, and in 1779 the Wintoun estate was again exposed for sale. As the property was of great extent, it was thought that it would be difficult to find a person able to purchase the whole, and it was therefore, by authority of the Court of Session, put up in lots. The first two of these, including the famous old Seton House, the chief residence of the family, were purchased by Mr. Alexander Mackenzie, W.S., who was common agent for the creditors of the company. [Mr. Mackenzie was succeeded as a common agent in 1789, on the nomination of the company, by Mr. Walter Scott, W.S., who at that time had as his apprentice his son, the great novelist and poet.] No objection was made at the time to the legality of this purchase on the part either of the Court or of the creditors; but thirteen years afterwards an action of reduction was brought at the instance of the company. The Court of Session gave judgment in Mr. Mackenzie’s favour, but their decision was reversed on appeal to the House of Lords. The Company not only raised the general question that the purchase was a breach of trust on the part of the common agent, but they brought special and strong charges against Mr. Mackenzie’s conduct in the transaction. They alleged that the manner in which the previous rental was made up was not satisfactory, and that the knowledge which Mr. Mackenzie had obtained in his official capacity of the condition and details of the property had been of material advantage to him. They further averred that the sale had been hurried through in an irregular and improper manner. According to the custom of that time the sale was advertised to take place ‘between the hours of four and six afternoon,’ a latitude allowed for the ‘want of punctuality in the judge, the clerks, and the other persons immediately concerned,’ so that five o’clock came to be considered the proper and real hour. On this occasion, however, Lord Monboddo, the Ordinary, before whom the judicial sale was to take place, having received a hint to be punctual, arrived at the Parliament House and took his seat upon the bench exactly as the clock struck four. Proceedings commenced immediately, and the first and second lots, having been put up successively, were knocked down to Mr. Mackenzie without waiting the outrunning of the half-hour sand-glass, as required by the Articles of sale. Several persons who had intended to offer for these lots found, to their great disappointment and chagrin, on their arrival at the Court that the sale was over. These allegations do not appear to have been taken into consideration by the House of Lords, since the illegality of the conduct of the agent was regarded as sufficient to vitiate the transaction.

In 1790 the new owner, Alexander Mackenzie, an Edinburgh Writer to the Signet demolished the old Palace of Seton and built the more modern mansion.  With an unpardonable want of taste and respect for historical associations, Mr. Mackenzie pulled down this splendid structure and erected in its place an incongruous tasteless building, which has frequently been used as a boarding-school, and is fit for nothing better. It is surrounded, however, by some fine old stately trees, and the gardens are still celebrated for the finest and earliest fruits of the season.

The destruction of the famous old castle of Seton was not the only act of Vandalism of which Mackenzie was guilty during the short time he possessed the property. A few hundred yards to the west of the castle stood the ancient village of Seton, which in 1791 was inhabited by eighty-six persons, mostly weavers, tailors, and shoemakers, each family possessing a house and a small piece of ground. This industrious little community, which for centuries had thriven under the fostering care of the Seton family, was entirely broken up and dispersed by the unscrupulous lawyer who had illegally, if not fraudulently, obtained temporary possession of the estate. When called upon by him to produce the title-deeds of their little properties, it was found that most of them had no titles to show, their houses and lands having been handed down from father to son through many generations. Those who were unable to produce their titles were at once turned out of their houses, while it is alleged that the few who possessed the requisite documents, and sent them to Mackenzie’s office in Edinburgh, never saw them again, and were, like the others, shortly after compelled to remove from their ancient heritages without receiving any compensation. Only one of the villagers escaped eviction. He somehow learned that his property had been registered when it was purchased, and he was consequently enabled to set at defiance the attempts of the usurper to rob him of his patrimony.

The lands in question were again exposed for sale, and were purchased by the Earl of Wemyss in 1798, at three times the price that had been paid by Mr. Mackenzie. The decision of the House of Lords unfortunately came too late to save from destruction the fine old castle or Palace of Seton, as it was called, owing to its having been frequently the residence of royalty.