Whenever you hire a car, remember that "full insurance" still has an excess. Cheap deals will not cover this, so you either need to buy the company's excess cover at the desk (€20 per day is not an uncommon price), or leave a big deposit on a credit card. You can buy separate cover for the excess, but the car hire company generally won't care about that, and they won't waive the excess on the basis that you hold the insurance.
The staff at the desk when you pick up the car are on commission to upsell you extras, whether that's excess insurance, breakdown cover, or whatever. Then when you bring the car back, at some less scrupulous companies, the person checking you in is incentivised to find tiny scratches that weren't mentioned on the checklist when you picked up the car and which they can bill you for "repairing". A well-hidden scratch, for example on the underside of the bumper, is like gold dust because they can bill multiple customers for it. They know that you are in a hurry to get your flight and aren't going to argue too much.
If you do feel like you are being ripped off, ask for the official consumer complaints book, which in Spanish is called "hoja de reclamaciones". This is a form that lets you fill out a complaint that will be looked at by the local consumer protection office. This is taken very seriously in Spain and dealing with the inquiry into your conplaint is a pain for the business. In fact, merely asking for the hoja de reclamaciones, and thus letting them know that you are aware of your rights, is often enough to make many issues disappear. It works in restaurants too.
Another near-scam to watch for is fuel policy. The cheapest deals sell you a taxi of fuel and you can bring the car back empty. But even if you do use a full tank in a week (not guaranteed in Majorca), you don't know the gauge, so you will probably bring it back with ¼ of a tank, which is profit for them. Look for full/full or same/same fuel deals, where you bring it back the way you took it out.
All that said... good companies at Palma airport that will treat you like an adult include Wiber, Hiper, Centauro, and Vanrell. But they will not do you a car with zero-excess insurance for €10 per day.