Okay, for your next purchase with "some guy" make sure that they show you the mod is in proper working order, and also if something used came to me "sticky" I'm not so sure I'd be very happy.
Do you have access to "some guy" to ask him for a refund?
Also, you might try some safer resources, but I'm guessing you may be in a country where it's hard to get equipment? Sigh. This is what I mean by the black market increasing crime and decreasing public health outcomes.... Still. Scammers can only scam if they get the opportunity, but hopefully you can find someone more reliable, somewhere. Don't hand over money unless you are handed working equipment. If you must buy, no cash deals, that way you MAY be able to report fraud, although if
vaping isn't legal in your country, I can see how that might not be the best idea....
I'm sorry for your bad luck.
Anna