The problem I've always found with buying & selling houses is that there are so many people involved it's easy to delay the process, and if one side wants to do that, there is precious little you can do about it (unless you are the seller with a number of potential buyers wanting a quick sale). Unfortunately for the agent, it's generally their name that gets tarnished.
I bought a place in a student town and wanted to delay the process to get nearer to the start of term to minimise my chance of leaving it empty. The solicitor and mortgage agent both offered to "take it slow" and were happy to take the blame, to the extent the said they were happy to be called by an irate buyer.
Likewise, when selling a place, agents have offered to slow the process up when it suited me.
It's a market, and people use all kinds of tactics. It's what happens.
Personally, I think that other countries have better conveyancing processes (I think it's Scotland where offers are legally binding; Australia you have a certain time to complete).
As a seller, you're currently in a strong position to negotiate terms with an agent - don't be afraid to ask.