Okay, several points.
The mossberg may be user servicable, but only if one has parts. There’s a lot of little fiddly parts such as the plastic safety button that can cause issues when non gunsmiths start mucking about in them.
The plastic triggerguard on the 500 is a weak point, the little tabs commonly break when unknowing people start disassembling the gun.
The left extractor is more a guide than an extractor, its shape is the givaway on that one.

The Benelli Super 90 is the best semi auto shotgun out there.
I have a Montefeltro not 6 feet away. Worth every penny.
H&K marked, its older and dare I say better. It wil function flawlessy with reduced recoil buckshot, unlike most semi auto guns.

Avoid all the chinko shotguns.
I had a 37 clone in for service, within 200 rounds, it had stretched its headspace almost .200″ and was suffering hull separations. The chinko guns are dead soft in most cases.
The 870 copies, little better.
The Stevens guns, pass, too crude.

Good, high quality guns are available used, such as the 37’s, old model 12’s and more. They may not be tacticool, but they still work.