Are we back to this again?
Lad over on askaboutmoney just got that offer: Tell the bank we agreed 310K and give me another 50K cash.
EA in on it. Cash to go to EA’s account pre contracts being signed 
He’s probably not paid his debts back and lived rent free for god only knows how long
What kind iof EA would participate is these shenanigans?
I can’t imagine a solicitor wanting to touch this, on either side of the transaction.
Not the first time I’ve heard of this unfortunately
Get the request in writing and go to the bank.
Agree to the deal.
Once your solicitor has the contract inform the bank and renegotiate directly with the Bank’s new EA
Could you get away with agreeing verbally (commit nothing to writing)
If the bank is happy with 310k feign shock when they ask for the 50k. Go to the bank and cry foul.
Be left in a position where you get the gaff for 310k
And leave a disappointed crook who knows where you live?
More likely the bank will discover that the market value (your willingness to pay) is 360k. Why would they then let it go for 310k?
Nothing would induce me to hand over that amount of money without a contract being signed.
Not to mention that said crook is still living in the property which you done a “deal” for with the bank, good luck with the plumbing.
There is nothing illegal about paying someone 50K in cash. They just need to declare it to revenue on their side. Is that too simplistic a view?
Giving that the seller is trying to pocket 50k and you have upset his plan - I think your worse case scenario might be a bit on the optimistic side 
What if the seller sells the contents for 50K ?
Now we’re talking, surprised the EA did not come up with that one.
So the sale price appears on the PPR as 310k and not 360k?
As a prospective buyer I fail to see the Issue with this (though as a taxpayer it’s aslightly different story).
Gift tax will be liable on the difference between the stamp market value and the sale price