After we purchased the building, she never cleaned the building, so we cancelled her service and asked her to sign a letter, stating if she didn't move out by end of May last year, she will pay $650 for her rent.

See a rent sign?

Two together make about $4000 and the third is job searching and her parents are willing to co-sign. 

That being said you could compel them to sign a waver that they don't want anything left behind if you agree to wave what they owe you.    

After selection of architect, work with him/her to get a well thought out scope of work.

Here is the code: "At the mutual inspection, a comprehensive listing of ascertainable physical damage, along with a repair cost estimate for each item, should be reduced to writing and signed by both parties.

This is incorporated in the asking price I give my cash buyer which motivates the seller to sign and sell quickly)11.

If I use the TREC contract, and then have the "assignee" sign the assignment contract (that has the assignment fee on it), then the buyer should hand me the check at that moment. 

Jeff Oberts and don’t forget to send your guests and make them sign the rental agreement (easier done on vrbo than AirBnB) that says “if you break your finger it’s not my problem” so these situations never occur.

There are firms that will setup this kind of specialized LLC for a reasonable fee and guide you on these kinds of questions.Typically these single member LLCs are disregarded entities and no S-election is made.