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I mean I would run a mile from that company. Glitzy website with very little actual detail. Spelling mistakes here and there. Website says they're in business over 20 years. Companies house doesn't have an exact match down to the address, but what I expect is their company was actually incorporated in 2021.
In fairness, trust pilot reviews seem decent.
Still, if I were you I'd go nowhere near. Get a proper damp specialist or a builder with lots of experience resolving damp issues.
i think it must be this sort of thing: a thermal imaging survey
eg. https://advanceddamp.co.uk/thermal-imaging-survey/
does that not sound quite reasonable? the damp areas will be colder so you can trace it on the inside and the outside