It would not surprise me if there were bots able to do this these days. AI is so advanced these days that anything is possible. It happens to many of us; especially a newer account. I was once offered more than the item was listed for, back when I first started selling. I wonder if the people behind this believe that it mitigates their karma if a seller is greedy. 

There are ways to lower your risk of selling on eBay so I would not be put off, but you need to learn how to lower that risk. One is to not sell Internationally which is fraught with higher risks.