I recently saw that a local tea store moved to Shopify.
It's more of a come in and drink tea shop but they do sell some bulk teas and teaware so a Shopify store can be nice supplement.
Funnily, they had a bootstrapper-ese approach to discounting.
In their footer, where most people don't look, they have this text:
Psst...use FIRSTORDER to receive 10% off your first order!
Then in their top and bottom menu they have:
ORDER DRINKS FOR PICK UP- SAVE 15% - Use Code COVIDSUCKS
It's not elegant.
It's not subtle.
It's not an official Growth Hack (TM) (C) (R).
But it's easy, effective, and any merchant can do something simple like that during slow periods.
Later on once they are more established they can do something more complex like using RFM to target their best customers but for now, something stupid-simple is good enough. And simple might be all they ever need.