I have seen lot of people having offer from multiple companies with offer letter from everyone and then joining one. As far as i know, unless you verbally accept their offer they dont give you offer letter. But is it good to deny one company once you accept offer verbally. Doesnt tha black list you in company profile? Please throw some light on this.
You can always ask for 3-5 days to give your verbal acceptance. One should not submit to the pressure from recruitment agencies saying that if you do not accept it now they might give it to somebody else etc. Companies do and can wait for the right candidate and similarly you can wait for the right company, offer too.
Even though it is not ethical to fall back on your verbal acceptance, we are living in a competitive and dynamic world and this does happen. I do not thing you will be backlisted. If they do, it will be childish.
Once I was offered job by company X , just a week before joining it, my manager in current company called me , and offered me salary more than what I was offered at X , I chose to stay with my current company .. the recruiter ( consultant ) threatened to blacklist me in consultant network as well as in company X .. after six months , I again got a call from X and not facing any issues ... I dont think blacklisting is done unless you do something harmful to company like absconding after joining etc..
[Astroturfing removed --MH] [ October 24, 2007: Message edited by: Mark Herschberg ]