99% of the stuff I collect is used. I'm super picky about overall condition.
On items I perceive as being rare, I'm more apt to accept condition issues. I do not refinish, but do try my best to preserve original surfaces on the tools and boxes I collect.
I hate to see decent salvageable finishes get totally ruined by a grinder mounted wire wheel brush.....

(pet peeve)
I have a slow process for socket sets:
1) Tools get a WD-40 bath, and individually cleaned with a either one or a combination of the following hand held tools depending on finish type and condition of the item being cleaned: stainless steel brush, toothbrush, scribe.
2) After the above process, light motor oil is applied, sits for a day or two and then gets a paper towel wipe down.
(Really rusty stuff gets an Evapo-rust bath and a hand held stainless steel brushing before the above steps. Not really expecting any preservation of original finish at this point unless it was unfinished steel to begin with)
3) Painted boxes: Crinkle finishes get a soft toothbrush cleaning with WD-40 and a soft cloth wipe down. Smooth painted finishes get a soft toothbrush cleaning with Simple Green and water while trying to avoid damaging any decals.
4) Smooth painted surfaces get an application of automotive grade wax.
5) Perform the above while enjoying an adult beverage and music of your liking....