Even if he got a killer deal, let me go out on a limb here and suggest that you can be picky about the mite issue.
As for them knowingly shipping them out - while I doubt they purposefully sent you a snake with mites, several people over the past month have come forward with their issues with BHB and mites. In that sense, the staff over there should be either extra vigilant, or as Spitzu stated, cease shipping until whatever control measures they are implementing have taken effect.