My husband has bought me three machines on eBay. I'm not sure why this is worse than buying anywhere else. It's probably just more expensive with shipping and all. I'd send them a message asking when it will be shipped. Or you could just keep checking the tracking number. It should update when things change.
I also had an experience where a seller hadn't shipped a book. Knowing it was going media mail (snail mail extreme), I waited for a couple weeks before emailing. She emailed me back with tons of apologies. The book had slid off the seat of her car and down by the door. She popped it in the mail that day. My husband and I have done a lot of eBay buying and selling. I agree with Faintly Artistic. Most sellers are nice, honest people who have jobs and lives well beyond eBay.