Yes, the estate can and should pay the mortgage to preserve the asset.If the named beneficiary does not want the gift, they would disclaim the interest in writing pursuant to local law and it would then pass to the next named heir or as part of the residuary.

You can buy a gift card.

Our deal was he was giving me the 3000 as a gift and I was going to sell my old car for about the same exact price m. 

The rent is the rent.. period.I would however compensate them for the hassle....gift card to dinner, movie, amazon...whatever.How much depends on how big of a hassle they went through and how long.

If they complain to you about a guest problem (noise, whatever) apologize, deal with it, then send them a big gift basket or something.Better yet, run your STR somewhere without an HOA

Baltimore, the gift that keeps on giving. 

Considering the holidays and people spending more money on parties and gifts, I was wondering if this would make it too hard to sell the property/would drive the price down due to lack of activity?

This would be perfectly fine and something we recommend if a parent wants to 1031 into a house for a child - Make a lease, collect rent, declare income, and then gift back to the child if you really don't want to collect rent.It sounds like the way you've done it is a little fuzzier. 

But a gift is OK.

I like the idea of a gift card to a local market or a nice restaurant for a dinner out.