If that were the case it simply shouldn't be listed as for sale and there would be no argument. At my pals greenhouse anything not for sale has a red tag and no price on it. It says that on signs here and there so everyone knows those are the breeders. Imagine walking up to a counter at best buy with a CD of a band you like and the guy says that's the last copy so you can't buy it. What kind of argument would you have, you have the $ and theres a pricetag...
My position is that it's discrimination and I would not do such a thing, yank something out of someones hands and tell them you just now decided it's not for sale. That certainly doesn't mean that I wouldn't try and talk an inexperienced or let's use the word "unprepared" person out of buying such a demanding plant unless they had build a chamber for it. I remember when you were growing highland neps by placing frozen water jugs in your tank every night, so everyone has to start somewhere.
As an ocasional vendor, far as I'm concerned, the plants are fine when they leave me, it's up to the customer to keep it alive. All my ads say that too!
If the little fink kills it that's not really my fault. I do what I can with educating my customers. I've got a website describing how I care for the plants (ok, I'm rebuilding it after the server crash but no plants are available yet anyway), how to build the grow chambers and every darn thing else I can think of to ramble on about concerning these plants. If they don't have enough interest to read it there's nothing I can do to force them to read it.
Enough of that, if we disagree we disagree no sense getting all loopy over this hypothetcal sale.
Yes, the charcoal is merely there as a way to add aeration, look for a charcoal which is about 1/2" long chips smaller than that size can become compacted. The brand Fertiloam is easily available and has larger chunks. If anything just tear open the sack at the store and look at it, most have a zip lock top so just zip it closed when youre done and no one will know.
Yes, be sure and rinse your materials (bark/charcoal/etc) with r/o or distilled water a few times to remove any excess salts. dust, etc that may be present before mixing and planting.