How does this scam work?

[migmogmash]

A man standing outside Tesco asking everyone going into the shop for a favour- he only has a voucher so saying you can use it to pay for shopping.

Clearly it’s a type of scam, but surely if they go in the shop with you then you’d quickly know if it doesn’t work? Or have I missed part of the scam sales pitch?

He was polite enough about everyone saying no, but standing by the only entrance to make it impossible to avoid him.

When I've seen similar he then returns the item for the cash.

Does he come into the shop with you though or does he just want you to give him money for the voucher then legs it?

I dont understand the OP enough to know what this scam is. Is he trying to give away a voucher? Sell it? If so, why is he coming in with you?

You could always alert the store's security staff as they will need to put a stop to him. It could be that he is sussing you out to steal a wallet/purse etc. That is why I would advise the staff.

Well obviously he sells you the voucher for less than face value, say it’s a £10 voucher, you give him a fiver for it, and when you get to the till it’s worthless and he’s legged it with your fiver. Why on earth do you think he’ll come in with you?

He’s trying to sell a dud voucher, no? Don’t think he’d come in with you