the most important thing about belt sanders is the base plate on the bottom. most belt sanders have warped, twisted or cupped base plates and will not sand well because of it. the first thing you need to do is remove the belt and the various thingies on the bottom and get to the main metal base plate. tape a piece of coarse wet/dry silicon carbide paper down on a flat surface such as your table saw and slide the sander back and forth on it.. now you will see the high and lows spots. you have to lap this so it is flat. do that and put your rig back together and happy sanding. my last Makita 9924DB's base was so cupped that there'd be nothing left if I just lapped it flat so I took it off and pounded it flattish with a hammer before I lapped it flat. another thing I do is soften the transition bends on the front and back of the plate to make them less abrupt and smarten up the outer edge to make it smooth and square. this helps a lot when you want to sand along a wall or other vertical surface and allows you to track the belt right to the edge and actually get full, proper contact with the surface you're sanding. also make sure the goodies that you took off to get at the plate are in good condition or get replacements to put on. those cork, graphite and thin metal plates etc must also be good and flat too.
it doesn't matter if you have the best or the cheapest sander, if you do these things you will get good results. the only things that matter is that the plate is flat and the belt will track. the rest is up to you and your skill. just remember that no matter what belt sander you buy, they are just like planes and chisels and not ready for use out of the box. they must be tuned up a bit to get the best results. cheap belts with a lapped joint should be avoided. they are almost never joined straight and will drive you nuts trying to get them to track, the bump at the joint is problematic too. stay away from them.
BTW, I start the sander flat on the wood all the time and I'm no rookie. I've been a cabinet maker for over 25 years. however, to each their own. it's the result that counts so do what works best for you no matter what others may say or do. if you like to spin the belt before touchdown go to it.
my pick for a belt sander it the Makita 9924DB it is light, turns fast, has excellent balance, a low centre of gravity and can run both 3x24 and 4x24 belts. it's sold as a 3x24 but I've never used one, I've always use 4x24 belts on it. it's fairly cheap too compared to some sanders although I buy what works for what I do. cost is a distant consideration for me if I consider it at all when it comes to tools. they are my bread and butter, not toys for weekend fun.