Sounds like you got some guy who was trying to resell them for a profit, and he ran out. He probably ordered you a new one from apple, and thats why its taking so long... I'm trying to remain positive about this.
Because, in all honesty, paypal/ebay are on YOUR SIDE 100%. If you never get the item or if it comes and it is different than what you were told, you fill out an affidavit and they refund you the money. It is a SUPER easy process and I couldn't have been happier when I got a broken pda that was supposed to be a new one.
On the reverse of that, if you are a seller on ebay... there is very little you can do you keep them from yanking money straight from your bank account if someone files a complaint against you.
I've been on both sides of this issue, and it is definitely in the buyers favor every time.
BOTTOM LINE: Do your research next time... and you didn't need to go to an apple store for an iPad, they're literally everywhere!