The whole process is stupid and instigated by agents who refuse to accept offers from people unless they've already sold their current property. Stops chains forming at a decent speed.
No, it’s not up to the agent, someone can accept an offer but it’s silly to take it because you have no idea how long it will take the person to sell, if they even sell...
It’s not an offer until the person can actually make good on it and by taking your house off the market will mean you may miss out on a better offer or one where the person is actually in the position to buy the house.
It’s also a waste of time viewing loads of properties if you haven’t yet sold, sure view a few so you know what you want but there is no say if a particular property is going to be around in the coming weeks or not.
What stops chains forming quickly is people don’t know what they want, have unrealistic expectations or others not making their properties available at short notice to people that have sold and the stupid ping pong you have dealing with someone via an agent when trying to arrange multiple viewings one after another or dealing with multiple agencies stringing viewings together.
The purple bricks system is 1000% easier, people just just put their availability online and you can just book in to view or you can request a slot if none suit. I don’t know why Rightmove doesn’t have this facility for all properties.