The key bit is "Let me translate this. Robin has been using someone else’s credit card for two years, and this other person realized that money was being withdrawn in the previous two years on a platform called Upwork without his consent." You'd have to be a pretty massive idiot to still trust someone after realising that...
Yes, because this is reeks of scam.
If you're in the same country and meeting physically... why on earth are you transacting via Upwork? Upwork was collecting 10-20% of the net payments. There's no reason to do that if you're physically meeting.
You use Upwork to facilitate international payments and for proof of work via their spyware when you don't trust the contractor. These two do neither.
You have to be obtuse and believe they just gave Upwork $1k from the goodness of their hearts... or there's some sort of scam. I don't know what the scam is; just this behavior is irrational to the tune of more than $1k if there isn't a scam involved.
You can still move it offline without saying anything but if you have a lot of credibility on either side you are doing what you can to avoid getting on the wrong side of Upwork.
So sometimes it is easier to leave it be. Also past $10k it is a 5% take which isn’t that bad if you’re rate is set to handle it and things are just cruising.
But they still seem to be on good terms with the client. If I understand correctly the problem is that they insist on getting paid through upwork:
"When things were not making sense, I still followed the rules. I could’ve easily gotten paid from Robin outside of Upwork. Heck, he was physically in front of me. "