You can check a bankcard on a scanner - bought for a few quid- to see if it's been used to travel and just have it set to take £100 out of each one you check in and be gone in quarter of an hour you'd get a few by then and off before anyone's checked their bank account and your away. Your in plain clothes, who's going to point you out? While thier distracted your ''colleague'' can have a look around their bags for a wallet, purse or mobile phone.
This sounds fanciful in the extreme - any evidence it has ever actually happened? I’d suggest anyone doing this in full view of on train CCTV, staff and the occasional BTP officer would be caught almost immediately. It’s also very straightforward to get funds lost to contactless fraud refunded by your card provider, so it isn’t the equivalent of someone nicking £100 cash out of your wallet.
I’d also ask, where does this reasoning end? Would you refuse to show a uniformed RPI your ticket on the basis they might be a scammer wearing a fake uniform? If they turned out to be real, as is
much more likely, you’d be committing a ticketing offence! At some point you just have to go with the most probable situation.
Various RPIs' attitude in the UK can't help. I recall watching a plainclothes inspector giving chase and then shouting at a young (presumably Chinese) couple leaving King's Cross tube, demanding to know why they hadn't stopped when he'd showed his badge. Particularly for people unfamiliar with the system, I'm not sure flashing a big medallion is clear enough by itself to (a) tell people what they have to do (b) give them confidence to get their ticket/wallet out knowing it's not a scam.
How is this a failure of the RPIs attitude? He’s clearly shown ID and made it clear the ticket needs to be checked - it isn’t supposed to be optional! AIUI people also regularly feign an inability to speak English as a tactic to get out of paying.
Some people on here have a rather “innocent” view of how dishonest an element of the population can be!