Several things that you will need to watch out for are overly worn pins which can make the loader sloppy,badly abused bucket which can not only be a problem in themselves but can also reflect the wear that the whole machine has had.You need to know the history behind the drive system,most skidloaders run on a chains like big bike chains and the chains as well as the sprokets can become worn and need replacement,not a big problem but something to watch out for.Control wear can also be an issue in the operation of the machine,and tire condition will be a cost if they are not in acceptable shape.As far as motors there is not much to be said other than the same thing you would look for in any motor applies here,oh and don't buy a gas machine make sure its diesel.Don't buy to old, there are tons of early 90s machine for reasonable prices.