yes.

you can sell a tower for full value 1nce using your builder, after that its 50% again.

dont know if anybody has hold 30 yet in 4.1.0.5 version.

here's a link of me doing it a while ago with my dif acc

https://www.youtube.com/watch?v=jW0PGbqxslc

Your Warcraft III username: Noobsmurf
Realm/Gateway: azeroth
Why are you banned: votekick abuse
Why you should be unbanned: a guy had lagged out which resulted in a 2v3.One of our teammates was not voting for draw so i voted yes to kick him too with everybody so we can draw.

Your Warcraft III username: necroman.
Realm/Gateway: azeroth
Why are you banned: had to leave bcoz i was lagging very badly and disturbing the game
Why you should be unbanned: i dont leave ever