You know how do you ask the seller if the title has no liens, all 337s and ADs complied with.....without offending the seller...
A title search will disclose any liens. As Ron 20 said, AOPA offers Title searches and there are other title search companies out there too.
Don't let the initial report of a lien scare you away. Lots of times it is just a paperwork issue and can be cleared up.
In the last couple months I have seen this type of thing in three sales.
As far as 337s and ADs, just have a knowledgeable A&P read the logs.
If something is missing from the books then the seller probably won't disclose the info even if asked.