Are drug dealers and prostitutes exempt from benefit fraud by Prison Widow UK

I have just returned home from a lady's house after supporting her through what I call a complete and utter farce. 
Now, I cannot condone what she did, although yes, I completely understand why she did it. Her partner was imprisoned 4 months ago, so having left her high and dry in debt with 3 kids to feed, she did a bit of cash in hand work as a cleaner - that's until someone grassed her up. Yes it would have been more productive to work and claim tax credits, or universal credit, whatever it's called these days; but she didn't. 
She's a good Mum, been through hell and high waters with her partner, and needed some quick cash. 
Today she was grilled by a benefits fraud person and the benefits fraud person was not impressed with a handful of questions I threw on the table. 
OK, the lady was guilty and threw the towel in. She'll have to pay back the money she owes them. Fair enough. 
Here are the questions I threw on the interviewers toes:

1. Next door but one to this lady, lives a group of drug addicts. Two men, two women. They all claim benefits but the tenancy is in just one person's name.
They all claim benefits, PIP, whatever it's called, and the two women work on the beat every night selling their bodies for cash in hand. As I understand it, prostitutes work on a cash up front rule, right? 

2. The people are well known to the Police. The rent is paid through housing benefit payments and in a nutshell, there's some serious wonga going in to that household, but the benefits department don't question it. 

3. A drug dealer lives on the same street. He lives with his partner and kids. Been at it for years and his woman claims benefits, rent paid for, free school meals and the rest of it. The authorities aren't interested in them either.

The interviewer replied that she couldn't comment. Why not? The questions are simple. Are drug dealers and prostitutes exempt from benefit fraud? 
They earn cash in hand money whilst claiming state benefits so all I wanted to know was, how does it work? 

Eventually the fraud person came out with a corker! She said they can't prove prostitutes receive cash in hand! But hang on a minute, if they followed them after an hour or so on the beat, wouldn't they witness hundreds of pounds being exchanged beween them and their crack dealers? Or do women/men prostitute themselves offering sex in vulnerable red light districts for free? Volunteer work? I don't think so. 
Hey, don't get me wrong, I'm not judging anyone here, I am asking a few honest questions as to why some people appear exempt from benefit fraud. No doubt it will have something to do with the 'professions' being illegal but what lucrative professions they are to screw the tax man to the wall! 

If I claimed Job Seekers, and I am half tempted to run an experiement, and declared cash in hand earnings stating I earned it through sexual favours working on the beat, would any monies be deducted from my claim? And how about tax credits if I worked 16 hours or over in the red light district? 
How does it work in Holbeck in Leeds? It's legal to work as a prostitute in Holbeck and I fully support it too. It is a good thing to keep women safe and councils across the country should follow their example in my opinion. 

Thoughts? Email me!