I've used Turnkey's from depotnet in the past. I can't really complain about the service. they provided a nice looking site and it was seamless all set up in less then a few hours.
However, I came to a conclusion about turnkey's. I had an impossible time getting my products on Google Base. Initially Google Base (Froogle, shopping, etc.) wouldn't take it because the data feed format of depotnet was not compatible with Google's ever changing format. So I went and made my own flat file and uploaded it to Google Base (shopping) but they knew that the site was a 3rd party site (since depotnet was hosting and handling all the data feeds) - basically I couldn't get on Google Base.
Another thing about turnkey's, make sure you ask to see a demo site, or a live site they host. I personally want my url strings to have the product name - like: mydomain.com/telescopes/celestron810telescope.html
Google seems to like that for better placing. when the url string looks like domain.com/telescopes/asdlkjflkasdj22i9sda9fasdfjkl2?kjasdkj.html i think it slows down your ad quality (if you're running paid advertising.)
All in all a turnkey could be a great option for a easy start up, but keep in mind, if it's so damn easy - then everyone is doing it.... which means your competition in that market just hit the roof.