Not in either 5e or 5.5e. In both the RAW says that if the DM has magic items for sale, potions will commonly be for "sale", but rarely for gold.
There is no RAW that says you can just buy potions for gold whenever you please.
They have a specific gold piece price (50gp) in the PHB. You can also buy them in AL.
I don't think what you are quiting was ever intended to apply to potions of healing in the context you are using.