My question is, he's been clean for the past 15 years no criminal record before or after that incident, has now a fiance and has been living with her and her 2 children for the past 5 years, has a good income and good credit.

Check the county records to see if the names match and you can also skiptrace the owner and call them to confirm they are selling the property - I wouldnt do that if your buying from a wholesaler though since it may look like you are trying to go behind their back. 

The experience goes with track record - do they have a history of doing this and being successful as well as having failures.

Is there a lien recorded on the property?

Look them up on the tax records for free and then use a free site like Spokeo to search info on the owner.

The promissory note and personal guaranty are private documents that don't get recorded.

Well, this is harder than it sounds especially when you're a beginner because you know no one and have no track record.

I can’t carry a gun I have a criminal record a remnant of a misspent youth  I carry pepper spray I’ve used it once.

I assume that this is a SFH so they probably won't have the best records.

Carrying costs in purchase and or rehab is financed, cost of capital on refi, re-recording, title, updated insurance, etc. their are many costs at play after initial funding then to transition long term unless your straight cash on the front end.