Large leak on bathroom floor

[whataboutbob]

I am rephrasing my earlier post as it was probably too massive for most to read through (thanks Wowfudge for persevering!) hope this is OK.
There is an ongoing leak onto the shower room of my Dad's student rental flat. Now the floor is sodden and it's spreading into the hall behind the bathroom. letting agents' contractors have been round and want £1390+VAT so about £1750 to look at the shower valve (which they say is likely source), change it, replace mouldy bathroom floor, and slightly raise shower box to prevent water pooling. My questions are
Is their diagnosis likely to be correct? - I suspect it could be the water pipes to the shower as they burst 2 years ago and some not very competent builders went in to fix them
Is this a fair price?
Would i be better going straight to a plumber and asking them to check things out?
Thanks for any advice. I have got back to the letting agents asking for a breakdown of costs for the proposed works

Can you post some photos? I still wouldn't go ahead without a second opinion. Has the quote come directly from the agents' contractor and is the contractor connected to the agents at all? You can check this on the Companies House website via their beta service for free. I am suspicious that there may be a cut for the agent in their quote.

sounds very expensive. I presume the firm has been chosen by somebody who doesn't have to pay for it. It would be wrong to suggest that they will be hoping for something in their Christmas stocking, but such things are not unknown.

Is the shower mixer valve and its pipes built into the wall and tiled over? This is why I often recommend surface-mounted mixers and pipes.

If you live in the area ask around for recommendations of an experienced local plumber. Do not call anyone with an 0800 or 0870 number.

Thanks so much wowfudge and PigletJohn. As ever your advice is most appreciated. Sorry I can't attach pics now because DH is away (I am so aware of how lame that sounds!) The pics emailed by the contractors are maybe not too illuminating they basically show a very wet floor in bathroom, a wet hall floor,a ring of damp about the size of a 1/2 grapefruit on the hall wall (behind the shower)and a bit of mould along the outer side (by the bathroom window) of the shower box.
I live 2 1/2 hours travel away, but will be going next week and will take a look and also get a plumber to look at it. I am a Which? member so will contact a plumber who is on their trusted traders page.

"damp about the size of a 1/2 grapefruit on the hall wall (behind the shower)"

that does fit with the idea that a concealed pipework joint is leaking, rather than silicone sealant.

Consider exposed chrome or stainless pipes and an exposed mixer when replacing, which will save you most of the trouble and expense.

meantime this all sounds pretty unusable. If there isn't a second bathroom in the property, you may have big problems. Do you have insurance to put your tenants up elsewhere while this is sorted? (do you have home emergency insurance for the property which may also help?)

Just updating. I got a plumber round who was well recommended on Which? local. He said it is not the valve, it's the sealant around the shower cubicle + "blown" tiles which is causing water to pool behind the tiles and drip down to the floor. He wants £1600 to remove damaged tiles, re tile, re seal cubicle, remove rotten wooden plinth and replace with new plywood one. That also seems overpriced. I am now looking at getting a 3rd opinion.
£1000 question- how does one find a competent tradesmen who does not overcharge? I wonder whether the fact that i am female, and not living locally sets something off in these gentlemen's brains which makes them ping and yell "sucker"? Or am I exaggerating the situation?
re the tenants SS I take your point. I feel bad they have already been inconvenienced and have only been in a few weeks (they're students). I will offer them compensation by knocking some money off rent when it's all over. Although I believe the place is habitable. Have recently put in a new boiler, and replaced all radiator pipes.
Any comments and advice welcome. I am emailing a neighbour of my dad's to see if he can recommend a plumber.