They are grumbling about the rent, even though I'm giving them a discount. 

My concern is that the actual people staying in my STRs are going to grumble because nobody cleans their room every day, there's no breakfast waiting for them, no pool, etc. 

If your house has been on the market since Sept and it’s in good shape, clean, doesn’t have a bad odor and is priced right in a good area it should have gotten rented already from my experience.

Next I cover with an oil-based Kilz primer which will seal in the nicotine stains and odor.

I'm with everyone else in the thread - unlike cigarettes, which leave a lingering odor, or hookah, which likely lead to nasty burn marks, pot smell leaves with the pot and it is usually consumed in a way that could only burn furniture. 

But I agree with you that urine odor is the biggest risk with keys.

No stains just the lingering odor that I don’t want to deal with.

However, on the inspection reports the inspector listed one unit has " a tobacco odor and stains present throughout the unit" and the other has "tobacco odor in unit that seems to be coming from the neighboring unit." 

They might be rude, ask too many dumb questions, seem high maintenance , have body odor, or just give me the Willie’s.

Take note if there are unusual odors in the garage or apartment.