I don't have/know specifics, but here are some generals;
1) Find out how many hours are on it. And, what was it used for? General, reasonable work, or was it taxed hard? Naturally, the lower the hours the better, but that doesn't always mean that it is in better shape. A high hour tractor, that was taken care of, can have a lot of life left in it.
2) Find out the sellers maintenance schedule, if you can. How often did they service, what did they use, what did they service.
3) You can check the oil, but that doesn't tell you much, other than if it is full or not. Diesel oil gets black, which is normal. Check the antifreeze and see if it looks clean, no rust color, full, and the normal green, orange, or whatever- make sure that it isn't just water.
4) Check the radiator- they are prone to get clogged up with dust and debris, which will cause engine cooling problems, and needs to be cleaned periodically.
5) Check the mechanicals- is steering tight, or does it have play, is the clutch tight and grabs well, or does it feel weak and pedal travels almost all the way out before grabbing- this will help you judge how much life is left in the clutch. Drive it- any gear noises, does 4WD work, does differential lock work, do all gears work, including ranges? Does the 3 ph go up and down without jerking? When you check that, you may have to push the arms down when you are lowering them- they don't have that much weight to them, so they don't fall very fast- that's normal. How does the loader function? Does it move smoothly, does it look square and level (sometimes they get bent or racked due to improper use), and does the bucket look good, or all bent up? Any visable leaks, especially fresh ones? A used tractor will invariably have some oil or grease on it, but fresh leaks indicate an above average flow of fluid, usually.
How does the engine sound? A diesel will knock and smoke upon startup, but will clear out. Does it run smooth through the rpm range, do you hear any unusual sounds? Does it smoke continuously, or just when you advance the throttle? A diesel will smoke when you impose a load, advance the throttle, inital startup, really cold (until combustion temps come up)- these are normal. But, if it smokes blue, or smokes continuously, then there may be problems. Any oil leaks, does the filter look real old, or like it has been serviced recently, antifreeze leaks, any jury rigging, etc.- does it look and run normal for it's age and hours, or does it appear to be advanced aging?
6) Tires- how much tread and cracking/checking, does the tractor look used and abused by the tires, or in line with the age and hours on the tractor?
7) Is the tractor missing any parts? Sheetmetal, safety devices, lug nuts, etc.- do some looking on line at tractors (there are tons of pictures), and familiarize yourself with what should be on your tractor.
8) Of course, do similar inspections of the implements. Don't gloss over them, and only focus on the tractor.
9) Take someone with you who is tractor savy, if you don't feel completely comfortable. It is VERY easy to miss something during the first inspection.
I'm am positive that I am missing things, but this is a start. The B7100 is a fine piece of equipment, if the price is right. Parts are available, they are solid, dependable, and inexpensive to run, and they resale well. Surprises can cost you a bundle, though. Be thorough.
I paid $3000 for mine, which is a mid 90's, hydrostatic, low hour, well cared for tractor. That probably isn't real representative, though, because I got mine for a bargain. Prices range high and low, depending on region, availability, and popularity. I don't know what to tell you about price, other than you know your budget, and whether it is worth it to you or not. You can always contact a local Kubota dealer, or something like it, and simply explain what you are looking at, and is it a fair price? They will probably be straight up with you.
Have fun, best wishes, and take pictures!
