Sounds like Pacific Heights! No good deed goes unpunished, right?
These tenants sound like professional deadbeats who have the art of freeloading down to a science. From what you wrote, they will keep finding faults and then at some point, use them for a reason not to pay or to offset against rent.
First, read your lease and suggest they do the same when they call with a demand. You are bound by the terms of the lease, no more. For example, you are not required to supply a new refrigerator unless the lease says you are. In fact, if the lease does not obligate you to provide appliances, tell them you will remove the refrigerator (just put it in storage for the next tenant), and they are welcome to purchase and install a lease of their own.
If it says you are, then unless you have a moron for a lawyer, the lease was drafted in your favor. It probably says you provide appliances but states nothing more about them other than they are in working order. Assuming that is the case, your answer can be similar - state you provided a refrigerator for them as provided in the lease, that they agreed it was satisfactory when they took occupancy of the premises (I trust you have a document they signed that said they did accept them and found them satisfactory - if you don't, create one and use it henceforth), but if they don't like it, you will remove it, and they may provide one of their own.
Another example, I don't have garbage disposals in my rentals because they are nothing but trouble. Again, unless the lease obligates you, remove it and plumb it straight the next time they complain about it. They can use the rubbish bin.
Everything they complain about, remove the source of the complaint as much as you can without breaching the lease with them.
Appeasement as a strategy never works - not in world diplomacy and not with tenants like yours. If the demand they make is not in the lease, simply reply that you don't read where you are obligated to comply with their request in the lease. Ask them where in the lease you are, and if you are wrong, you will address it. You need to take a hard line and strict interpretation of the lease, and here is the reason:
If the demand(s) they make is(are) not written in the lease and you comply with them, they become part of the lease, anyway! That's the way courts have ruled. Once that happens, you are in a non-win situation. That's the reason you should make the rent due date specific, accept only the full amount, and stick to it.
Don't be confrontational with them about it; just point out that you don't read where you are obligated in the lease, and if it is a "grey area", take the position that protects you. I am always very nice. I say something like, "I'm not trying to be a stickler, but I have a business to run. This is your standard practice that applies to everybody." If they ask you to make an exception, just reply, "I wish I could, but I can't."
Document everything you do in that unit and keep good records. When you correct something that the lease does require of you, prepare a fill-in-the-blank form that you have them sign each time that shows the date that they brought the matter to your attention, briefly describes the matter, shows the date it was fixed, and states that their signature (make sure it states one party signing is sufficient) shows their full satisfaction with the action you took. Have two copies and leave them with one.
Sometimes, if I have a good tenant, I give them a break or do something for them that is not in the lease. However, when I do, I still document it in writing and state specifically that it was a one time exception as a courtesy and does not change the terms in lease in any manner whatsoever and that they acknowledge that fact. I have a line for them to sign at the bottom acknowledging the letter so it is in writing.
Documenting everything is just good business regardless of the kind of tenants. As indicated earlier, I am always very nice about it. I simply explain, I am a nice guy; I just have a business to run and have to follow the procedure as a practical business matter. Only a tenant with an evil agenda will object to that.
The probability is high that at some point, you are going to end up in court with these tenants. However, if you adopt the practice I have described herein, you 1) reduce the odds because you remove any grounds they may have, (deadbeats know the system, believe me) and 2) if you do end up in court, you have a paper trail that demonstrates you complied with the lease, addressed any concern they had in a timely fashion to the extent the lease obligated you, and that they were fully satisfied with everything you did.
Above all else, you want to set yourself up as the reasonable party. Despite what any laws state, unless the judge involved is a jackass, and that rarely happens, they rule with the party that impresses them as the most reasonable and the ones that make it easy for them. Paper trails and rational conduct make it easy for them. They hate it when it is is "he said, she said" situation, and they have to be subjective.
If they quite paying rent or don't pay on the date specified, serve them with notice regardless of what excuse they give you. They will try to make it your fault with some complaint or another saying they will not pay rent until you fix whatever it is. Your response is always, "I am addressing that as we speak, and you are still obligated to pay rent regardless. The lease does not let you off the hook for rent" (unless like I said earlier, the attorney who wrote it for you was a moron).
When their lease term is up, do not renew (hopefully, they have no renewal option) and given them written notice to vacate strictly in compliance with the terms in the lease. Do not let them hold over no matter what.
Finally, in the future, screen your tenants better. Use a screening service and check references. Go two landlords back and/or more. The most recent landlord will make them sound great no matter what because he/she wants rid of them.
Stick to your principles for leasing. If they flunk one of your criteria, move on to the next applicant. If you rationalize, you are setting yourself up for trouble. The demand for rentals is high across the nation so no reason exists to compromise.
