When I see rate fluctuations for similar duration / services, I just assume the provider offers different rates for different times of day. I see plenty of MF and RM profiles where a provider offers a discounted rate before 4pm or 5pm since after 6pm is likely peak demand for them. Or perhaps during a dry spell, a provider may lower his posted rates to drum up some business. There could also be instances where reviewers might incorrectly be including the additional amount they tipped the provider when quoting the rate paid in their review.
If it seems amiss it seems it would be better to just move on instead of questioning it which just seems inherently crass, not unlike the client version of a clock watcher provider.