Depending on their response to that question, I reveal who I am or I pretend I'm just scouting the neighborhood for deals. 

When phone screening: I like to ask people if they are familiar with the area the apartment is in, it tends to spark a conversation where people reveal things about themselves: good and/or bad. 

When someone has enough balls to ask your age (let's be honest, the question alone is them trying to insult you), I tell them I'm happy to reveal my youth if they are willing reveal how old they are first. 3.

Once the rehab is complete, a 3rd party inspection will reveal any issues that may not have been addressed. 

Maybe they are lying about the property and duing the diligence reveals that.

Many foreclosures don't reveal everything or how much they know.

Several buyers were willing to pay $2.2M-$2.4M, however, because this was an assignment, the revealing acquisition cost caused them to renegotiate.

The FHA says that examples of such problems include but are not limited to the following: Missing handrailsCracked or damaged exit doors that are otherwise operableCracked window glassDefective paint surfaces in homes constructed post-1978 (because of lead paint hazards)Minor plumbing leaks (such as dripping faucets)Defective floor finishes or coverings (worn through the finish, badly soiled carpeting)Evidence of previous (non-active) wood-destroying insect/organism damage where there is no evidence of unrepaired structural damageRotten or worn-out counter topsDamaged plaster, sheetrock or other wall and ceiling materials in homes constructed post-1978Poor workmanshipTrip hazards (cracked or partially heaving sidewalks, poorly installed carpeting)Crawl spaces with debris and trashLack of an all-weather driveway surface=================There are many areas, however, where the FHA does require problems to be remedied in order for the sale to close.Electrical and Heating The electrical box should not have any frayed or exposed wires.All habitable rooms must have a functioning heat source (except in a few select cities with mild winters).Roofs and Attics The roofing must keep moisture out.The roofing must be expected to last for at least two more years.The appraiser must inspect the attic for evidence of possible roof problems.The roof cannot have more than three layers of roofing.If the inspection reveals the need for roof repairs and the roof already has three or more layers of roofing, the FHA requires a new roof.Water HeatersThe water heater must meet local building codes and must convey with the property.Hazards and NuisancesA number of conditions fall under this category.

In addition to what others have posted above if you listen to the questions a tenant ask it will reveal things about them as well.

Roof jobs typically reveal rotten wood/etc that needs to be repaired after the shingles come off.