It's certainly not irrational to be wary of a system proven with a rift of fraud & scams , where a person's word means nothing & false claims are the normal , what would be irrational is not being sceptical of everything associated with the internet .
Ben Franklin said long ago, "Do not believe anything that you hear and only half of what you see" He was wise beyond his years indeed!
Look at the ad the op posted. If you’re not seeing the red flags, you shouldn’t be buying stuff online.
It's not the red flags I missed or didn't see, it's what the op failed to see, along with payment loss details.