I've rented apartments in Italy, Spain , Denmark ,the UK and Paris for 20 years, mainly in Italy.
I've used Airbnb, VRBO, and TripAdvisor and Booking.com; and have had only one of 23 that wasn't very good.
In Europe you will rarely find a dryer in a rental apartment, and if they have a "combo" w/d, it's usually not that efficient.
Washers there can take up to two hours for the quickest cycle, so plan accordingly.
The quickest I've found was a place in Rome that washed a big load in 30 minutes!
A miracle!
Some washers in warm countries will be outside on the balcony or patio, with a waterproof cover over them, so ask if you don't see one in the photos.
Ask the host to SHOW you how the washer works, and write it down.
Some are not intuitive to get working!
If there's a washer, there is usually a fold-up drying rack.
Get a flat with a balcony or outside space, and you can dry your clothes in the fresh air.
Some flats in Italy have racks or lines outside the windows attached to the building.
Don't drop your undies in the street when you hang them out!
Rent an apartment with loads of photos, and ask the host to send you a "map" or blueprint of how the flat is laid out.
Some listings have this in their photo list.
It might say two bedrooms, but one might be the main living room; and you can't always tell from photos, as they sometimes show the same one bedroom with different bedding and lamps to make it seem like two different bedrooms.
Study the photos carefully.
Note if there is a photo of a washing machine, and what the shower looks like.
Look for a shower that is enclosed in a cabin or with glass doors.
Those are smaller than what we are used to in N. America, so if you are a bigger person, you might find it a bit of a tight fit.
If it's a "wet room", or the shower head looks like it's over the toilet, give that place a miss.
The bathroom will be soaked all the time.
Some flats have an en suite bathroom; but that's no good if it's the only bathroom, and you want two bedrooms for more guests, as people will have to walk through the main bedroom to get to the only bathroom.
If you like a flat but can't see on the photos what you are looking for, write to the host and ask for confirmation of a working washer, reliable WiFi, etc.
Look at Google Street View if you have the address of the place, to see what's around the area.
Don't rent a flat over a bar!, they can get noisy at night, though in my experience, people do not drink to get drunk in mainland Europe.
(I'm sad to say that the UK is a different story.) :(
Try and find a place that does not face a busy street with shops etc.
Lots of shops have early morning, as in 5 am, noisy clanking garbage collections.
Look for lots of reviews, good and bad.
Some people complain about the silliest things, such as the TV only having Italian channels. Really??
Ignore those.
Try and rent from a Super Host.
Look for reviews that say the owner or host was very helpful, and visible.
I would be leery of renting a place where you have to pick up keys from a shop or agency storefront, and you never met an owner or host.
Not that it's dodgy, but what if the keys didn't work, or you lost them and couldn't contact anyone.
Also, you need the owner/host to show you how things work in the apartment.
Make a list of your must-haves.
Mine are: reliable WiFi, an outdoor space, and a working washer.
Now that I have bad knees, I can't walk up five flights with luggage nowadays, so I look for one floor up from the street, or something with an elevator.
Some European buildings will have elevators, but you might have to walk up a flight to get to the first elevator stop.
If you are fit with good legs, go for a higher floor for the views!
I like to be able to get to a main train station easily too, for daytrips.
You can map out the area and even look at local bus routes on Google Maps.
Good luck!