I have a few friends who are in the market for a long-arm machine. I'm no expert, but I have owned two so I do have a few opinions that I can share that I hope will be helpful if you happen to be looking to buy a LAM.
Like everything else, you get what you pay for. If you want a "good" machine, wrap your head around spending at least the same amount that you would spend on a small economy car (assuming a new machine). There is just no way to sugar coat this - these are expensive toys.
When you get a LAM, you are also getting a frame and this is an important consideration. My recommendation is to NOT get a frame with plastic working parts. Plastic threads (as in screw threads, not sewing threads) will eventually strip and other moving parts will eventually break. Go for metal all the way. This will rule out a lot of cheaper frame options.
Also be sure the roll bars are one piece - do not get roll bars that are one or more pieces assembled into the roll bar. They have more propensity to sag in the middle and the screws come loose and need tightening (or gluing, or something!) from time to time - a nuisance.
I have a motor on my frame that I can use to advanced or roll back the quilt on the frame - I love this option so if you can get this for your frame, I would suggest you say "yes"! I didn't get the hydraulic lift that would raise and lower the frame. I sort of wish I had, so if you can get this option, give it some serious thought.
Most machines come with regulators. The regulator on my first machine never worked properly and I got tired of trying to get it fixed so just learned to use the machine without it. This is possible, but in a 21st century world, why go for a 20th century machine capability? Be sure the regulator on your machine is a sturdy component of your machine and not a flimsy add-on.
Test drive. Every brand has its unique characteristics and feel, so take the ones you are interested in for a good solid test drive to see what the differences are. The best place to do this would be at a quilt show and fortunately these days most of the major brands show up at the bigger shows so you can test them all on the same day, which is good, because, just like the famous Pepsi/Coke taste tests, the differences are readily apparent if you can "taste" them all more or less at the same time.
Take home the spec sheets or get them on-line and do a thorough comparison regarding the details - standard vs optional components/features. What are the warranties like? Read on line reviews.
Check out local reps/service for your machine. In the last couple of years, the availability of dealers and local servicing has really been improving, but still has a way to go - at least in Calgary. I expect in a few more years (due to demand) there will be a full range of options available within a reasonable distance. Having said that, if there is no local dealer for your preferred machine, check that the service from that brand's "Mother Ship" is good. Most are - but ask around for personal experience (in Calgary, come out to our Long Arm Group meetings - 2nd Tuesday of the month @ 12:30 at rotating locations - contact me for details).
So those are my suggestions of what to consider when you're looking for your LAM. Good luck and once you get one, you're gonna love it! 💗💗💗💗