Gazumping – this term describes an improper and illegal act where a seller of real estate, once agreed to sell to a concrete buyer (usually with a concluded private purchase contract), suddenly increases the sale price and accepts a better offer  for sale given by another buyer who usually has no information about the initially signed contracts.

See also examples for such problematic property purchases: http://www.bulgariandeals.com/viewforum.php?f=6&sid=343f3aa7a041c8722f94d7f59e066f12