If they sell it, and they are in a 0% tax bracket, there is no tax for them.Potential problems:once you gifted it to them, it is theirs, and they don't have to sell it, and they don't have to give you the $50k profit, eitherif they do give you back the $50k, it has a potential of being busted by the IRS, even though the IRS will probably never know about itbut if they do, you run a risk (pretty small, but still) of a criminal case against you, which is something I personally would never riskthe property becomes subject to claims of your parents' creditors.

I've had two occasions where the reference they listed told me not to rent to them because they were violent, late payers, or too needy.Not doing a criminal, credit, background check, which might have revealed criminal or credit problemsBeing slow to evict (mentioned by others)Believing their sob storiesAccepting partial paymentsFailing to document every conversation or interactionNot walking through the property to make sure they're taking care of it (I now walk through every 9 months so I can see problems in different seasons)We've found crack pipes and other paraphernalia after they moved outWe've discovered piles and piles of trash (some bagged, some not) in closets, basements, sheds when trash cans and pickup service are included in their rent - all they had to do was carry it out, at no cost to themWe've Found smokers, pets, extra peopleOverall, I've had great success as a property investor. 

Dept. of Justice has advocated to sellers/buyers for many years.