AirBnB, Booking.com & especially gentrification suck, but if I were to rent out a place, some things i'd (not) do or skimp on.
Condiments, I will never understand paying for a nice renovated apartment with a kitchen, where the owners are renting it out to you for weeks, yet there is 0 salt or pepper or cooking oil. Those items do not go off for months or even years. They cost so little. It is a small service that saves your guests time and money and having to leave behind half full packages. Same with a little washing powder and washing up liquid.
I never hope for more than those, but of course if there are a few more staple type condiments, even better!
Garbage bags, same as above. Every guest will need a few. Who wants to buy a roll of twenty soon after they arrive only to leave behind the vast majority when the vacation is over?
One or two sharp knives and enough slightly decent crockery and pots is a bit of must. It is naff to have too few plates, cups or cutley, so that your guests constantly have to do a small amount of dishes. I have rented a few places that had such blunt knives that I went out to buy any old cheap as chips but at least sharp knife. A blunt knife can be very dangerous.
If an apartment is obviously outfitted with not only very few but also the absolutely cheapest and worst Ikea kitchenware, that is also daily tiny irritation. Besides, they are more likely to be broken quick and need frequent replacement.
As an example: I truly loathe these mugs below. Spend 50 cts more and you can buy stuff that is just fine! But not these tiny volume/low capacity, thin and hard to hold and easy to burn your fingers on alleged mugs,..
Not enough towels or sheets, and having to ask for them and taking long to get them. Essentially if stuff starts to smell a little or you have less comfort than at home, it becomes a bit strange and unpleasant.
Shower-head mount issues. I have been to so many places where the shower holder had only one position, too high or too low. Sometimes both. Like it wasn't apt for me nor for my partner and we have a 30 cm height difference,... An adjustable / sliding holder is about €30 at Ikea, I got one at home, works great.
Many times also the single non-adjustable holder was made from very brittle chrome-plated plastic like the one below, and was cracked or loose on the wall plug. An actual metal variant of this holder below (or even two) truly does not cost much money:
Without an ok or even broken holder, you end up showering a little worried or holding the shower-head with one hand for much of the, or even the entire, shower,.. very meh.
Lock issues and key issues. Several times I have experienced that the owners initially only wanted to give us one key. Despite knowing we would both be renting and sharing the apartment, for almost three weeks. We also like going out separately sometimes as well. We don't share just the one key at home, why would we want to do that when we are on vacation?
Many times I had apartment door locks that were installed incorrectly, very low quality or extremely dry and corroded. If you have to fight, jiggle and mess with the door/lock every time you open or close up, and always think it might not quite work or the key could bend or break,... not a very vacation feeling.
I am not a pro-locksmith, but I taught myself a lot about doors, locks and keys during about a decade, they still have my interest, I am sometimes watching stuff on the topic and taught myself a little lock-picking fairly recently etc.
For that reason I can always tell that the (rental) door or lock issues usually constitute a simple and fast fix. Just a bit of adjusting or perhaps chiselling a bit of wood or maybe a 2 minute replacement of a €12 cylinder, no biggie. But I don't carry WD-40 and a tool set to my vacation destination!
LED Light bulbs, even low Kelvin = pleasant sun-coloured ones have been cheap and durable for years. Yet so many places I have stayed at have extremely bright and overpowered plus really blue / high Kelvin light bulbs. Why? They consume more electricity, make everything including food, people and entire apartment look worse and are really unpleasant, especially in morning or late at night. Weird.
Battery issues. It is great that almost every place now has a little or big flat screen TV! We always take our SSD's and watch our favourite shows and films. But not if the remote for the TV (happens with Air-Co remote too) has totally depleted batteries. A tester is real cheap as is a bigger pack of batteries. No guest wants to run out late in the evening after a whole day travel to hopefully find some store that is open and that sells them,..
Plugs, for what I guess must be cost-saving motives, so many apartments that have been totally renovated are still really deficient in the placement and especially the amount of wall sockets/plugs!
Guests have kindles, phones, laptops, need a bedside lamp a bit close etc. It can even be costly for the guests, say if you have to have your laptop charging with the charger cable stretched half-way across the middle of the room since it is the only way to plug it in and have your laptop on the table while you work,.. You might find entire thing crashing down if you are unlucky or don't pay attention for a bit.
It has come to the point that I always bring two small/flat 2 meter extensions with four plug sockets, one for my partner, one for me. I have never regretted bringing those, use them in almost every apartment and in train to ensure my devices are charged and a little safer.