I'm not sure it's really the most upfront thing to do, but you do have a point -- if it looks like a small amount, the occasional buyer will probably assume it really is. Nothing stopping you from putting some water soluble vitamin powder in there if you really want to. Just make sure you double check that you don't put one a person can actually take too much of in, of course.Just saying it doesn't have to be a choice between too much or too little: just tell them exactly how much actual MDMA there is and they get exactly what they bought and wanted whether they get some vitamin C with it or anything else.