Bank's require co-signers for a reason: the person with poor credit is unlikely to be either unwilling or unable to pay (or both).  

I require rent for people to stay in a property, but that doesn't mean I am unwilling to help them work through a difficult situation.Money is important, but hurting people to get money isn't worth it.

If they are unwilling, communicate that to the Landlord and try to negotiate an early termination or see if they will allow you to help find a replacement tenant to take over.

They broke the lease after 7 months, stating that I was unwilling to fix the shower.

If the seller is unwilling that is often what agents do so they can get paid.

So the checkpoint if you will, is if the prospective tenant is willing to submit to the background search in the first place and don't accept anyone who is unwilling.

Deferred maintenance (e.g. roofs) are things renters already expect (table stakes) and are unwilling to pay for.Then you sound like it's not really a big deal. 

I also spoke to the auction house to see if I could get the LLC credit charge reversed and charge the deposit instead to the trust account, but they were unwilling to do that.Be that as it may, the distinction here seems to be between loans and contributions, and I would say things that are paid back are loans, and things that are not paid back are contributions.

I also try and take pictures if seller is willing (I had one unwilling) and write down notes.

They didnt fall through, the seller was unwilling to come down on price to cover repairs... so there you go.