Why is it so difficult to get a refund on a purchase that I paid in full for?

[jocwag_20]

The seller asked for an additional $610 when i purchased it, there was a $174 shipping and handling fee. The seller said EBay would return funds back to me. 
This has been a slight horror transaction! Not to mention, the seller says they had strep throat after EBay contacted them, I guess

[shipscript]

Something is wrong here and there is a lot of missing info.

Is this something purchased on eBay, or could this be a scam that was found on Facebook or elsewhere?