I get you - there is an element of coffin chasing about it.
Their point is that these are estates left in purgatory on account of the benefactor not leaving a will. So they state that it would be almost impossible to know if you were in fact a potential beneficiary, particularly if you had never even met the distant ' long lost' relative. They portray this as a service and some people go to them speculatively to see if there's anything out there for them to claim.
I certainly had no inkling that I may've been in line for a pay out.
It is coffin chasing they have obtained a death certificate which is relatively cheap for them. Then they have written to every financial provider on their list, some wont tell them the amount until they know they are dealing with the executor. So if you get contact from one of these companies about a relative just do what they have done. Write to everyone especially major banks the post office etc there is standard wording that solicitors use while representing an estate and doing this you can do the same. Or just get a solicitor to do it for you that wont be charging 20% of what can be a very large sum.