if you absolutely need something you can flash in clockwork,you could restore the backup you made of your stock setup(you made one,right?) then wipe data/cache/dalvik and reboot. this will leave you at the "touch android to begin" setup screen. of course,it will be a rooted version,wich may or may not matter to the buyer.
the other option is to do this:
http://androidforums.com/incredible-all-things-root/181255-how-downgrade-official-2-2-a.html
if you rooted with unrevoked,youll still be s-off after,so if THAT matters,youll need to run unrevokeds s-on tool.
since whomever buys it isnt going to have a warranty anyway,i personally would sell it as a rooted device. may increase your available market
