New instruments are always nice to purchase. There’s just something very special about taking a new instrument out of the plastic wrap in the case. Trumpets are simple instruments. Dents can usually be removed, but you will usually be able to see where they were. Also, keep in mind, a horn that’s used will eventually get a few dents. Wear in the finish uaually can’t be fixed cheaply, and it’s just not worth the expense for a beginning or intermediate trumpet. Professional instruments are usually worth replating, but it will cost $400-$500. By the time you calculate the cost, it’s usually better to just go ahead and purchase a new instrument.
Professional instruments will hold their value better than beginning or intermediate trumpets. My trumpet that I play most of the time, is actually worth more than I paid for it new fifteen years ago, and it’s well-used. Just make sure when purchasing a used isntrument, that the valves are in good shape. If they are plated valves, make sure the plating is not pitted. Also, make sure that they work well after they are oiled. Problems with the valves can be difficult and costly to repair.