Best Way to Get Diamonds?

Returned to AJ after a long time and it seems kinda hard to get diamonds. I've listed RIMs and etc for 1 diamond, and listed bigger items below market value, yet I still have a hard time selling them cause there is so much competition with other users (shop wise).

Everytime I go in the township there's always at least 7-10 other people advertising their shop. Not that it's a bad thing, it's just hard to get people to buy even when listing for genuinely cheap prices. I'm just wondering if there's certain things people look for/are easy to sell? :)