The only thing I have seen is once a year (May) where there is a independent study done regarding convenience gas stations (Casey's is one of the predominant brands studied, although other convenient type gas stations are also involved.) I think the convenience store industry commissions this study. It is done like a myster shop though and then the results are reported in an industry magazine (I have actually seen the results mentioned in news articles) Anyway, it involves gas and inside goodies and then some questions about signage seen, how many coolers, etc. It has been done by the same company year after year (originally based in Canada) who now has Kern doing most of their scheduling. I did a zillion of these the past two years becasue for some reason they aren't popular. I don't know if Kern will take over the scheduling of these are not this year (of if they will even be available.
Hope that was vague enough yet informative