There’re so many markets to go to in Chiang Mai. The most popular would probably be the Saturday and Sunday Market and daily night market near Panthip plaza. There’re even more markets when you go outside the Old City and most tourists that don’t go here to trek, usually go to Chiang Mai to shop.
If you’re into selling novelty products, I think that this is a good base to start from since the nearby small villages in Chiang Mai seemed to be manufacturing a lot of the products you see in the shops such as painted parasols, wooden carvings etc.
Aside from the usual clothes, bags and shoes, here’re some products that I think you would find interesting.
Some stalls are also selling lucky amulets, some items that seem to be old relics (I dont know where they got those) and a lot of HMong inspired items.
Make sure that you bargain hard but politely since most of them are willing to give those items for a lower price.