You are not renting from AirBnb and you are not renting from Homeaway; you are renting from either random individuals or from management companies that represent random individuals. There is nothing wrong with this, but you should understand the relationship. Most (many?) apartments will be listed with multiple agencies. Each agency (Homeaway or AirBnb, etc.) has its own set of rules and safeguards and you can factor those into your equation.
To increase the odds of a positive experience pick a place with a high number of excellent ratings. A place with only 5 reviews, all very positive, in my mind isn’t as sure a bet as a place with 100 very positive reviews and 7 not so positive reviews. So go for quantity.
Sometimes it’s hard to discern, but if you can find a place that is professionally managed, that’s a better bet in my mind as well. I think you are better off with a business man than you would be with a guy renting out dead aunt Louise’ apartment for beer money. Renting directly from the management company might save you a few dollars and might get you better service as they can afford to do so without having to pay the listing company fees; but you get fewer safeguards in return.
Most apartments will have a name or there will be some unique text in their description. Take that name or that unique text and Google it to find more listings and reviews and maybe the management company.
Finally, it’s always about location and amenities. Don’t believe the “close to” statements. Find it on a map. If its summer you probably want an A/C (much better a permanently installed one as the little portables don’t do a lot of good). What floor is it on? Remember in Europe the first floor is called GROUND, so the 1st floor is really one flight up. Is there an elevator?
And I guess, most important; is it legal. Some cities have cracked down on short term rentals - but not many. It’s an easy thing to find out, just Google. Oh, and you get what you pay for, never more and often less. If its too good to be true .......... it is.