What are different way to get exp to level up your shop? Is selling items the only way?
#EXP
cedar hemlock
stuck meteor
Merchant xp is from shop sales, (except after you get Talents there is Questing: Roadside Wholesale which give a FRACTION of xp for inventory overflow forced quest sale. This is prety deep in that talent tree; so, not available until mid/later game.) Dragon Invasion Supply counts as a shop sales, give xp. Vending machine sales count as shop sales, give xp.
.
Non-merchant xp includes for Heroes & Champions, from questing; for Workers, from crafting; for Mundra, from fusing; for pets, from feeding. But only Merchant xp is what levels your Merchant.
stoic drift
A good way to figure out what items to focus on would be to use the datasheet. You can sort by Merchant EXP and find what items are the best for you to craft or buy from the Marketplace.
?sheet
(since Dyno appears to be having issues)
stuck meteor
Sell em all, let God sort em out!