I've had a few mules and several more horses and they are expensive to own, but if you want them, then get them.
What I look for in a horse or a mule is an animal that is calm and rideable by anyone and everyone. I don't want an animal that has to have an "experienced rider". That means they do $hit you don't want to deal with.
Get one that will load in a trailer without any fuss. It sucks to have to spend an hour loading an animal that doesn't want to get in and go. My last two horses would load and unload by themselves if the gate was open. They would calmly step in and move to the front and wait for you to close the gate. Then at unload they would back out and stand there waiting for you to take them. I'd make sure they would load before I bought them. Load them and unload them several times and try them out before you commit.
There are lots of other things I'd look for but these two are on my short list when it comes to hunting animals.
They must pack meat, hides, and antlers with no b.s. I would make the guy you are buying them from prove that they will stand there and let you load all that stuff on them before I'd buy them. I own a taxidermy shop and I will take them to the shop and put all sorts of dead animals on them before I'll take them home for keeps. If they snort, buck, bite, kick, or run like hell, you keep looking! There are lots of animals for sale that will do the job. Don't buy one with problems you will have to fix. Especially if you're not a horse or mule trainer.
Last but not least, I take them on a ride up a trail somewhere new to them and make sure they don't spook or shy at the site of "ghost stumps" and scary imaginable things off the side of the trail. I go to lots of new places in the mountains far away from home and I don't need any crap happening on the trail, especially when I'm riding after dark. If the horse or mule jumps out from under you at the imaginary sight of a dark object off the trail, don't waste your money.
I know these habits and traits can all be fixed by a competent mule trainer, but........I'm not one, and it don't sound like you are either so buy the best so you don't have problems. It's worth it to check them out thoroughly. More expensive is not always better either. If they'll do all the things you want them to, and they cost $1,500 then you got lucky. My last two good ones, and I mean they were good ones, cost $1,000 each. The guy was tired of feeding them and wanted to get rid of them. They pack, ride, load, haul meat, stand there while you shoot,(not off there back either) and my kids can ride them both. When I say the haul meat, I mean they haul meat from elk, deer, lions, bears, buffaloes, and any other kind you care to put on their back.
Hope this helps. I"m sure the real cowboys on here will set you straight, or rather the mule skinners will, but this will get you started.
DeerBeDead