I've been thinking on this a little bit and have started to look at it from a different perspective. First, operating under the assumption that the MSC's post was completely accurate, the $5 fee was clearly stated as the result of the item not being in stock. Therefore the $5 payment was correct. (The OP has not returned to either acknowledge or refute this, so there is not a reason, at this point, to doubt the MSC's word.)
However, the shopper certainly feels justified for being frustrated with a 45 minute visit resulting in a whopping $5 in pay. None of us would be doing this were that the norm. I don't know the details of this shop, but I do have parallels in different shops:
For one MSC, I used to visit apartments for $40. This would typically mean a 20 minute visit and a 30 minute write-up, amounting to an average payment of roughly $47/hr. (not including travel time). Not bad.
However, if the apartment manager no-showed the appointment, I waited for the required 15 minutes, had a ten minute report to do and was done. So, that's roughly $94/hr. That's a score.
Every once in a while, though, the manager got really excited bout showing me around and I could spend 90 minute on the property. Of course, the report would then also take 90 minutes, for a total of three hours of work at just over $13/hr. I felt screwed.
The point is that, going into a shop, we really never know what is and is not going to happen. Sometimes it works our really well for us and sometimes it does not - that's the nature of contract work. So, before I take a shop, I ask myself if I can live with the consequences if it were to go sideways. If not, I move on. If so, I take the job, so my best work, and see what happens. Of course, on a new job to me, I just don't know. I have to recognize that there is a risk involved.
Hard work builds character and homework is good for your soul.