As someone who was an estate agent for 10years but no longer is... it looks perfectly reasonable to me
They have to spend time and money taking appraising your property, photographing it, compiling details, putting those details into a format for market, taking ID, paperwork for the house, liaising with yourself to sign off the details before market.
Then they spend money on printing the details, talking to buyers about your property, meeting buyers at your property, negotiating a sale
Then there's the job I did for 3 years, progressing the sale, liaising with solicitors, other estate agents, the purchaser, the broker, the surveyor etc etc
The minimum I'd expect is 16 weeks as the only agent to try to sell
If, after spending time and money on trying to sell your property they find you a suitable buyer who offers an acceptable price that you've accepted and THEN you play silly buggers and decide you're not selling, then IMO fair enough they should get something after all they have fulfilled their end of the agreement!!!
If you want someone to plaster up some of your crappy photos and do no viewings for you, or negotiating or progressing of your sale, then just use an online "agent"
Honestly some of these comments are the reason why I don't want to do that job anymore. People are so entitled.