One annoying thing about disabling right click is that I often use it to "Open Link in New tab" or in a new window.
When sellers use this script I can't do that. It might not stop me from buying from them, but it's pretty annoying.
Also there are still a lot of easy ways to steal the description even if you do this, so it might slow someone down a little, but not at all if they know what they're doing.
You can for example do "Ctrl+A" then "Ctrl+C" and you immediately have copied the whole page. Then you just have paste it into Word or anything else to quickly edit it whatever you want.