I looked a WC the other day which wasn't flushing.
She'd be told but some know-it-all who can't do owt that all it needed was a new diaphragm in the syphon. This was true. Technically.
It also had rusted over screws from cistern to wall, rusted bolts on cc plate, no doubt a doughnut resembling a fossil, one of the above pictured POS iso's (fitted on pipe with no play and terrible access) the cheapst possible, oldest looking inlet which I'd already decided I'd replace too as a matter of course. And while I'd got through explaining why I'd change every part, fitting and fixing that could be changed I think she felt she had let a conman in. She declined my price and let me out. I wasn't fussed. I do a lot of this stuff and can't be bothered with people who won't trust that I know what needs doing.