Does anyone know of an app that will let you create discounts based on either the vendor or the items' SKU?
Shopify's discounts can only be set by either collection or individual item. I sell customised items and once an item has a custom design added then it is no longer the blank item in the listing and it is also put into the designer's collection so the discount no longer applies. The SKU and vendor are the only item details that remain the same.
Freddie here from the Shopify Support team, happy to help.
I've looked through our Apps store, and it looks like the main app that stands out to be able to achieve exactly what you're looking for, would be:
That app looks to be the best option, but you can browse through the other discount apps available right here.
Otherwise, hopefully we see other developers or merchants post alternate more custom solutions here. You can also look to reach out directly to a Shopify Expert for help in a custom solution.
Let me know if this helps!
Shopify Support - firstname.lastname@example.org