I buy and sell on eBay. This thread reminded me I bought my Janome on eBay. I didn't know how to sew so it sat in the box for a couple of years (moving and building a house), I was happy to find out I bought a $1500 machine for $169, it was still in the original packaging. It works great!
I just bought a Brother XR4040 because it is lightweight, to take to classes. The seller has great feedback, and the machine came with 25 yr. warranty. I don't know if I'd have to send it back to him if it needs repair. I fired it up and wound a bobbin and it seems fine. I really do need to go play with it. I bought 25 bobbins and 1/4" quilting foot on ebay on Wednesday. It was less than $14 for all of it. I have no fear of buying on eBay.
Many times I will check a product locally and then use that model/serial number and buy on eBay for much less.
In addition to the advice about using Paypal, I would also send an email to the seller and see if he/she communicates with you before you buy. I have had "power sellers" ignore my email and did not buy from them. I want to know if there is a person there that cares about my purchase.