And good old standard contract law says that there is no contract (therefore no duty on either party) until the valid offer is accepted.
And guess what, you can rescind the offer if want, then it is no longer valid. IT IS AN OFFER, NOT A CONTRACT!
However, it would appear that you have notice of their rejection of your offer, as evidenced by their "sold" advertising, which means you can conduct yourselves accordingly.
Until both sign parties sign a purchase agreement contract, neither side is bound by an offer. Usually, an offer in real estate begets a counter offer (which really is a rejection of the first offer and a new offer to you, which you may now accept or reject.)
A verbal offer in a real estate deal is only as valid as both sides want it to be. A purchase agreement contract for real estate absolutely must be in writing, or it is unenforceable.
Don't stress, if your offer was low, then at worst you will get a counteroffer which you are free to reject.
And besides, there are tons of contingencies in the purchase agreement contract through which one could wriggle with a buyer's agent, but again, you have not signed a purchase agreement, so chill.
Shoshana (who did well in both her Contracts class and her Real Properties class, but has put the information out of her mind as she concentrates on her last year in law school. And please do not consider the above information legal advice on what you should do. It isn't legal advice.)
P.S. If this really was the house for you, then you would be feeling stressed that they aren't going to accept your offer. That the revese is true is telling about the timing and this particular house. When it is the right time and the right house, you will go the extra mile to get it done.