SEDO is a well respected domain marketplace ... they have over 9 million domains for sale (minus about 10% that the owners have forgotten to delete after they expired lol) ... they are their own registrar so if a domain "goes astray" they will be in a good position to investigate about it ...
the procedure goes like this ...
after you receive an offer , you can either accept it , counter-offer , send it to auction or cancel it
if you accept it : they notify the buyer ... the buyer pays ... they put the funds in escrow ... the transfer agent asks you to either transfer the domain to the SEDO account on your registrar (recommended) or to send him the authcode so that the buyer can complete the transfer to his registrar
the buyer can pay by Credit Card (up to $500) ... by PayPal (3% surcharge for amounts more than $500) ... or Wire Transfer
the seller can be paid by PayPal (free to receive funds since it is PayPal Mass Pay) ... or Wire Transfer (no Wire Transfer fees)
the procedure can get completed quite fast especially if the buyer pays by PayPal and there is a push to SEDO's account at the registrar and not a transfer ... many times though the transaction takes a while ... this is usually because the buyer delays sending the money in and/or because SEDO "does not work" on weekends ...
if you counter-offer : you can haggle back and forth until you reach an agreement for a sale or auction (see below) ... bear in mind that most first-offers are usually very low (mostly $60 or $100) while also most counter-offers are usually quite high (to leave room for haggling)
note: according to SEDO ToS you are not obligated to accept an offer even if it is the same as your expected price (unless it was fixed price) ... technically (in the ToS) it is considered as
a basis for negotiation ... but it is kind of considered as "bad business tactics" if you don't accept an offer matching your asking price ...
if you send it to auction : the initial offer stands as a reserve ... if there are more bids , more money for you ... if not , the domain is sold at the initial offer ...
if you cancel it : you cancel the transaction ... the buyer can only bid again if he contacts SEDO and ups his offer reasonably ... but someone would do that only if they are really interested in the domain so it is not recommended (unless the buyer keeps sending you lowball counter-offers for an obviously valuable domain)
fees are 10% (with $50 minimum
for most major TLDs) if the domain is listed in your SEDO account , regardless if it is for sale or not or if it is parked or not
... and 3% (with $50 minimum) if it is not in your SEDO account (SEDO Domain Escrow for Outside Transactions)
if it is in your SEDO account and also parked at SEDO , the fees are 10% only (the $50 minimum is waived)