Forgot to add....

If you really want to get an idea how often something sells, either look at the listing revision history (the earliest dated revision will give you the minimum amount of time the listing have been active for), or view all of a seller's items, sort them by newly listed, then check for the listing you're interested in, as it will display the date the item was listed.

Then, if a listing has been active for say 8 months and 108 were sold in that time, you can see they sell an average of 13 a month (it really will only give you a rough idea, in either case, as a listing could have been created in January, but you won't be able to see if it was available for sale the entire time since then - eg sellers can put their stores on holiday mode and hide items from the site, or they could have been out of stock several times for who knows how long in total).