Teesping is a huge success right now, and I know there are tools out there to see what your competition is doing, especially Teeview | Teespring campaign viewer
But I figure nothing is ever too much. So I'd like to give you guys a little Google search string I use to find out teespring campaigns that have the characteristics I want to.
To be completely fair, I took this string idea from Jack Duncan, if I'm not wrong, who used this for a totally different application, but the concept is pretty much the same
site:teespring.com " 20..99999 sold towards goal of 10..99999" "ended on */14"
With this string I will find only campaigns that sold 20 units or more, that ended this year.
Just to illustrate a little better,
If i wanted to find, say, campaigns that sold between 50 and 65 shirts, which had a minimum sales goal of 30 and ended last month, I'd use this string:
site:teespring.com "50..65 sold towards goal of 30..99999" "ended on *4/14"
Sales numbers can tell you a lot about scalability of a campaign, when you infer the audiences and angles that could be taken with a given design concept.