I also recommend that when you get something, you pull up the assembly manual, a couple of beers and disassemble the entire thing down to the last screw. Make sure you keep individual components in ziploc backs along with their all their screws. Clean them all and then rebuild it all from scratch. Depending on the complexity and how well you catalogued all pieces, it can take 10-12 hours if you're new at it. Make sure to track missing screws, broken/damaged pieces, symmetrical screws that are different, stripped screws or holes and anything else that is amiss. This will tell you very quickly how accurately the seller represented their rc vehicle. You should plan to replace some parts depending on your tolerance for things that are wrong. Also remember that metal on metal parts should have grease. If they don't or if the diff oil/shock oil is dirty, then the owner probably didn't do a very good job maintaining it. Sometimes it's hard to tell the age of the diff oil because there is supposed to be grease and oil inside the diff.

Be very careful with shims since they are so easy pull apart and not see where they were originally. It's also very easy to drop little (and big) pieces and lose them. Don't disassemble over carpet.

Once you get good at it, you will be able to do it much more quickly and be able to replace broken pieces without disassembling everything.