Pre-existing Tenants

[Jimmy NA]

I have been looking at a couple buildings lately that I am interested in purchasing. The buildings pass my expense/income standards (and the price is right) but I am worried about the quility of the tenants. I have no definate way of knowing if the tenants that are already renting there are paying or behind on rent. I could ask the owner, "are the tenants paying?, of course he will say "yes." How do you approach this problem?