So, how does a prospective buyer find out where seller has the bikes? eBay has strict rules on sharing that kind of info, as one could just end run the eBay platform, and they don't make a dime. I'm surprised the listing hasn't been taken down.
The amount of vetting of the bikes (how many are stolen?), and the person (how do you transfer tens of thousands of dollars to someone in a trustful manner?) would take much more than a day.
The odds of this not being a scam are non-zero, but that's as far as I'd go.
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If someone tells you that you have enough bicycles and you don't need any more, stop talking to them. You don't need that kind of negativity in your life.