So, you're talking about being the successful bidder at a lender's foreclosure auction where the property is currently under contract for sale, right? I'm going to assume these facts.

Tony's answer is quite good. The right of redemption is cut off upon the issuance of the Certificate of Sale (not to be confused with Certificate of Title). So, the moment that happens, the former owner of the property no longer has any ability to sell the property.

There are a few technicalities we could get into for academic purposes, but the bottom line is this.

Even if the former owner were to find some clueless buyer who actually goes through with the purchase after the auction, the Certificate of Title you get from the Clerk will supercede the buyer's claim of ownership. Basically, it would be fraud on the part of the former owner, and the buyer would have to go after him/her for remedy.

You would be fine.

~ Jeff

I had an answer prepared for you but decided to speak with one of our panel attorneys. Check back here next week for what will be I am sure a clear answer.