It will take some time, and worst of all, it will cost you money if you do not take immediate action from the beginning. Your lawyer will have to sue the seller and ensure with the aid of the tribunal that restitution of legal fees as well as recovery by way of damages is possible. Don´t forget that the 'tenant' in this case has not left a deposit and he may well take a flight on the day before the sentence is passed with the eviction order, after three months, after the legal expenses you have incurred in and the loss of profit for not having been able to rent out the property, or even worst, rentals you have had to pay since you had no property.
Where the seller is to remain in the property after you have purchased, make sure you withhold a sum of money equivalent to at least four months rent on a similar property, which should include your lawyer´s fees.
If the tenant vacates on schedule, you duly refund the amount.
