NamePros, Sedo, GoDaddy, DAN, Afternic...
How long is a piece of string, how saleable is the domain. You'd get offers all day for 4 letter dot coms, a strong and truly understood 1 letter dot com (if you're prepared to accept a cheap enough price), how bad do you want to sell? People buying bulk domains, flipping in bulk, with certain contacts...this stuff happens. If you don't have a network or structure to do this, then no. IMO