Overheated hermie, frothing, brown liquid

This may be hard to advise in general. It depends on the temperature of the pet store and the temperature of the crab at present. Either way, try to cool down the crab very slowly. You could cool it back down to the temp in the pet store, but it may not need to go down that far. Maybe cooling down the crab to the midpoint of the two extremes will be enough. For example, if the pet store is at 65 degrees and your crabitat is at 75,, then cool the crab back down to 70 degrees. But remember to do this very slowly, probably over a few hours.