The EA needs you to prove his case.
Case for what? The best the estate agent can hope for is to get them on breaking an exclusivity period. ‘But I found them a really good buyer!’ is not admissible evidence in a court of law. No one is obliged to sell their property, even if they offer it at a certain price and someone offers that price. They can change their minds at any time prior to final exchange.
If you give a statement, IF this goes to court then you would be asked to turn up to be cross examined.
Good God, she’s not going to be up before Rumpole of the Bailey. The chances of this even making county court are pretty minimal.
There will be a clause in the seller-EA contract that if seller pulls out of a sale for no reason then they are still entitled to their fee.
But there IS a reason - they got a better offer. It doesn’t matter that, according to the OP, the estate agent doesn’t believe it was genuine. What court is going to say ‘Sorry, even though it’s perfectly legal to accept a higher offer before a sale is finalised, we don’t think it’s very nice or fair, so you’ll have to pay the agent’? Don’t forget the estate agent agreed to act on this higher offer - that’s why he went to the OP asking her to counter-offer.
Despite what some on MN think, ‘They weren’t very nice’ or ‘But it’s not fair!’ won’t stand up in court.