The redirect forwards the user to the buy points page with a relevant message and if you click back, the wall post is still there (although this may be Firefox being helpful). I did the condition check with an select statement with substitution in brackets on the #__alpha_userpoints table, I assume there is no better way.

Next release will let you specify "goback", "return", or "reload" for the URL giving some better control over where the user is sent.

The only problem I found was when using multiple triggers in 1 action. When I changed the single triggers to the following, none of them worked:

Yeah, multiple triggers per action is currently bugged. Next release will fix that (this week I hope).