If you would like an Estate agent to treat your potential buyers like scum then I fully recommend Stephensons. For example I rang up to ask them to let the seller know we were going on holiday and that she would need to get back to us with a response to our offer and they insisted that the seller already knew this even though I was telling them this for the first time!
Also when the seller rejected our initial offer I asked what sort of offer they may be open to and they told me haughtily "that isn't how it works, you have to make a higher offer". I'm sure that counter offers are quite common in house buying!
Even if we were not going to be able to buy that particular house there may have been another property on their books which we might have bought. However the agent was such a patronising, rude and unpleasant person I would have struggled to phone them up. Of course vendors do not have to accept offers but agents should still be polite to potential buyers.
Also on Saturdays viewings are conducted by temp staff who may not know anything about the house and might not have a key to the back door!
Our offer was 8% below the asking price so we were not wasting anyone's time. Don't waste yours and choose an Estate agent that is at least slightly pleasant, it's a difficult enough time to sell your house right now as it is.