You have everything to lose by doing a lease purchase. In over 75% of the cases, the deal does not close. Think. You have paid a lump sum down, right? You will probably be asked to pay a higher than market lease with the agreement that the "excess" will be applied to the eventual purchase price, right?
An unscrupulous seller may be able to sell the house to another buyer at any time before the deed is transferred into your name. He can also mortgage the property to the hiltt, making it more difficult if not impossible for you to qualify for a large enough mortgage when it comes time to buy. You can't buy, he keeps the proerty and your money. What if the seller gets into financial trouble and loses the house to foreclosure? How many liens, judgments and vioations will there be on the house? Even perfectly scupulous owners can die, or get divorced, which means the house can end up in an estate or marital dispute. If you elect to proceed with the lease/purchase, make sure you hire a REAL ESTATE attorney, not the guy or gal who handled that traffic ticket for you!