I hope these criminals do get caught and agree that they should be checked out first before any work is agreed.

I believe if you are caught by this you can be fined for illegal dumping. My understanding is that the onus is on you to verify that any company you use for waste removal is properly licenced.

Warwickshire Trading Standards warn of Rogue Rubbish Collectors who are checking out Welford on Avon and surrounding area's asking if they want their household rubbish removed for a fee who then dump it a few streets away or elsewhere. If anyone is suspicious of doorstep traders you need to contact Citizens Advice Consumer Service.
The website has the helpline number to call, [url]www.citizensadvice.org.uk