1) I'd worry about an apartment shop when the starting offer is $12 - especially with it being targeted.
2) With all the directions I've seen on apartment shops, if you show up and the target is not available, you still get paid. You might have to wait 30 minutes hoping a no-show returns, or do teh tour with another agent. However, if you make an appointment and make the trek to the complex expecting to do a tour, you should get your money.
3) With the agent cancelling while you were en route, things get dicey. I had that happen to me once, but I did not get the message until after I had arrived. I was paid for the visit.
I would put together a nice email to the project manager and explain the circumstances. If turning around the moment you got the message would have meant wasting an hour, you should have a good negotiation. However, see point #1.
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