What a zany thread - why would anyone list a domain for $100 (minus 15-25% commission), especially a 2-word .COM that actually makes sense? Usually I would say "just sell it" but $100 for that domain looks like an obvious typo error.
In answer to your question, if you renege (just say it was a typo and you meant to price it as $1,000 - I've had that one fed to me before, so all's fair) and Sedo might just go away.
If they don't and require the transfer to go through, then if you don't they'll close your account there. How valuable your Sedo account is to you is for you to decide.
And no, you can't renegotiate for $500, which IMO is still too low.