........... Do they hassle recently bereaved to produce evidence of there finances for the last 7 years?
Yes. Only it isn't "hassling" it's applying the Tax Laws!
I had a mate up in Scotland who apparently "owned" a 5,000 acre estate that contained a load of forestry, a few houses, two farms and a 22 room mansion. There was a slight problem in that he didn't actually "own" many of the valuable things that were kept in cabinets and hung on the walls of his mansion. (He even had an original Matisse painting in his toilet!)
Rather than pay the Inheritance Tax that his predecessors had owed HM Revenue they had been allowed to "donate" a shedload of paintings, ivories, statues, bronzes and other valuable articles to the government. The value of these goods were then off-set against the Inheritance Tax due so that no money actually changed hands.
Here's the rub.
NONE of these very valuable articles actually left the premises, the "owner" (i.e. the government) was responsible for their insurance, the original owner still has the benefit of their presence, members of the public may only view the articles by appointment and their status is contained in an unpublished "catalogue" held in London (Somerset House I think.)
An artist friend of mine tried to track down the Matisse and discovered that the "catalogue" was a random collection of works of art with no actual grouping such as Artist's Name, Location, Date of Acquisition etc. In other words, finding out about any particular item is a major task.
The whole system falls into the "Nice if you can get it." category; or "scam" if you wish to give it a more realistic name.