This has happened to me three times - latest one I viewed on Saturday afternoon, rang agent today to find the vendor accepted an offer already; they seemed surprised that I should even want to know!
So is it not normal practice to check people who viewed and say just to let you know it's going to go under offer do you want to offer too? Is that not how it should work? I saw the documentary last year where they were saying agents will tie up a sale with someone who is taking a mortgage through their broker, without getting all other offers first and not actually passing on all offers anyway - just to get the extra commission. Anyone else had this experience?
Edited to say I could understand it more if you'd not got back in touch for days; also I just remembered this happened in a slightly different way on one occasion before where I had made an offer, waited to hear and then they said no someone has offered higher and its been accepted. This was within a day of viewing so not when there had already been a back and forth of offers.