Theory: Finding play testers is hard because most designers don't treat them with respect.
As someone who playtests board/card games, I can say that I'm not willing to play test for most people a second time. They have not done their homework. I have no desire to do it for them.
1) I expect the game designer to have played it solo a few times before bringing it to the group. "Pretend" you don't know what the other person intends to do.
a) Does the game feel like it has interesting choices?
b) Does it feel like the choices matter? (This is often more important than their actually mattering.)
c) Does it play in roughly the right time frame?
d) What happens to players who get behind? (Make a conscious decision.)
If this is too much work for the designer, then why should the playtester spend his time on it? The designer is in effect trading their time for that of the playtesters. I won't playtest for these people again.
2) The designer should know when to stop the playtest.
If the game is clearly broken, what else can they learn right now that is a good payoff per playtester time? It is time to stop.
3) The designer should be open to feedback. For many games, the early feedback can be very negative. Accept that the playtester is trying to help you, even if you don't agree with the comments. Record them anyhow. Looking at the pattern of recorded comments later may help identify the one small change that fixes everything. If, instead, the designer gets defensive or authoritative, they won't test for you again. Clearly you knew better, why did you even ask. Realize that both initial and after significant play opinions can influence how a game is received.
4) When a dimension was identified as broken during game play or in the post mortem, I don't expect to play the game again until it, and any parallel cases in the game, are resolved (fixed, eliminated, etc.). Again, this comes back to respecting the playtesters' time.
5) Realize that playing to break the game IS part of play testing. If there are pathological corner cases, you do want to find them. If you know the game is shaky enough that people should not do this, why are you asking for their help? Either fix the issue first, or be very clear up front. I know X,Y are broken, so we won't use them this game. I'd like to see if Z is working now.
