Well, a couple things:
1. REI's techs have to be certified to work on and install bindings, just like any other shop. With that said, some techs are good, and others, well...
: Don't discount them totally. You may have gotten THAT guy. The guy that used a 4.1 bit instead of a 3.5. I've seen it here more than once.
2. When I was a tech, I would occasionally see a binding tear out. 90% were Markers, and probably 75% were the heel pieces. I've never liked Markers, and the only way I'd ever use them is in a system where they did not have to be drilled. Some people love them. I'm not one of those people. The heel screws were always too close together for me. That said I HATE the single front screw design in the toe. Those and the new Salomons give me nightmares. What a DUMB idea - the torsional forces are huge there - what 1 more screw going to hurt??
3. You said "bit of a rush" -- does that mean you waited in the store for them to be mounted? Sometimes that can lead to "in a hurry" mistakes.
4. Did you give them a good inspection before you skied them? Were the screws sunk in? Was there any gaps? The tech should have looked for that too, but you know...
5. "Short screws" -- I never really know what to think about this. Every binding I ever mounted came fresh out of a box, so all the screws were there from the factory. I just never can see the "wrong screws" argument, but maybe I was just lucky. Most shops don't swap out screws on new bindings unless they add or remove a lift plate. every binding I've ever worked on came with them already semi-mounted. Also, with a quick glance on the hill, a patrol might have a hard time determining if the screws were too short, especially if they had maybe never been screwed down enough, or had pulled back up into the binding holes. I know I would have a tough time saying that for sure. Be careful how much faith you give to that "diagnosis". Just sayin'...
Anyway, you deserve some kind of compensation. It just depends on what you go after. I'd personally set the bar high - start with an all new setup. Then bargain from there.