Just a few preliminary thoughts - this is a beginner list and of course not all inclusive.
1. What recourse do you have if title is not as they say? How deep are their pockets if you have to sue? You will want to do your own title research first - sort of a "trust but verify" scenario.
2. If vacant then you are lucky. If vacant when you see it but not when they first bought it make certain they took proper steps on clean out etc. When you take a home at auction you do not automatically get their "stuff" too. Make certain everything was handled properly and documented properly.
3. Make certain the sale looks "clean" and "makes sense". If buying from an HOA sale or sale from a 2nd mortgage - these can be overturned by a judge (first mortgage sales can be also but not as often) - so know what you are getting.
4. Certain liens can carry over after a sale. Some mechanics liens etc are not always extinguished.
5. You will have to pay up the property taxes. Not everyone remembers to check this and understand there may be thousands owed.
6. Certain IRS and other tax liens may remain and carry on the property - have your title rep check this.
7. Do not take any "out of the ordinary" properties. Major code or environmental or building and safety violations carry over to the new owner (that's you) - stick to the easy stuff.
- Those are some initial things to think on.