Myson Marathon 80c?

Job done properly no complaints on that just the price
for a days work and allowing £100 materials wear and tear of vehicle etc.

A friend has done it against advice to ask for a rough price to change rad valves give or take £50.

Charged £90 for 3/4 hour call out and minor work on boiler which I think he switched on only, following day £750 for changing 8 angled manual rad valves for new angled manual rad valves which were bog standard cheap looking valves. Time taken to complete including going to get the valves, 9am-6pm. Got her to sign the receipt when he's gone she looked for it to see what was done and show me, receipt gone with him so she has no receipt and no record of work carried out. Total stung for £840. Can't get hold of him to ask for the receipt back and not a copy. My thoughts are ''Rogue trader" as she made the mistake of telling him she's a widow with disabled son which makes me think its open up his till further than it should be.
Fair or a stitch up? West Sussex area.