Many but not all people who sell 3 star have mastercraft alchemy. It is recommended that you do, as you will save a lot of gil in the long run. However, one of your biggest customers for Terminus Putty will most likely be from non-master crafters, who buy the mats and find a crafter to make the equipment for them. This is cheaper than buying the equipment directly but it is more time consuming and riskier; I know many crafters who will simply say "too bad" if they NQ your stuff.