price a new one. get all the details you can from the dealer about what comes with the machine; free repair and maintenance; what happens if the machine turns out to be a lemon, etc. do they include freebie extras like classes, attachments and other gadgets?
compare the cost of new - which will offer some warranty protection - against the cost of the used one - which you will buy as is. factor in the value of any free service, classes, attachment, gadgets and other goodies.
if you consider buying from the total stranger, insist on testing it for at least 30 minutes and that she give you a written agreement to take it back if you find something wrong with it in the first 30 days.
you may decide you're better off buying from the dealer.