A person that I met recently has asked me if I could make some payments in his name. He's offshore and has bad signal. He would give me his account details, bank account, and password. Is this a scam?
Yes, it's a scam. You should stay far, far away. I'm assuming you haven't actually met this person face-to-face, since you said he's "offshore." So, you "met" by receiving an email from him (or a text, etc). Let me know if I'm wrong.
In situations like this, I find it helpful to imagine myself in the other person's position, and try to figure out how he got to the point of sending emails to random strangers with a request like this. When you think it through, it becomes pretty obvious that this plan makes no sense.
Does he not have friends or family that he could ask to do this for him? Why would he trust his bank account details to a complete stranger otherwise?
If he can't get signal to make the payments himself, how was he able to contact you electronically?
Setting aside the question of his signal, how did he get your contact details? Does he know one of your friends? Why didn't he just ask them to do this instead?
Has he been sitting around plugging random email addresses into his computer until he found one that didn't bounce back as invalid? Does that sound like a solution any rational person would engage in, especially when he's planning to divulge bank account information to the recipient?
If he really doesn't have any personal friends to ask, why can't he just contact the people he owes and ask about making special arrangements, by the same means he used to contact you? Even if he can't make payments that way, they want the money he owes them, so they should be willing to help him find a way to give it to them.
If nothing else, he could give them his bank account info and let them withdraw the money themselves. (It's not any riskier than asking random strangers on the internet, after all.)
So yes, this is a scam. I don't know exactly how it works, but were I in your position, I wouldn't want to find out by participating.