Sadly I have seen this happen before on eBay.
I had a buyer who explained that they had to pay by e-cheque due to a financial emergency. Of course this was fine by me and I only needed to wait a few more days for payment. I noticed that the buyer had won other items during this time, and in their feedback they had a "false positive" from a seller complaining about slow payment. The buyer responded saying that they did pay straight away but the seller re-listed the item.
So the seller either didn't understand how e-cheques work or was an impatient so-and-so like your seller.
I'm sorry this happened to you.
That seller is a nasty person for doing this. I just wish that Paypal wasn't constantly lauded as being "instant" because e-cheques do exist and they're perfectly valid.