Hi Alison,
I really don't think it's in the camera. However, I am getting a new one for my birthday :D
I currently shoot with my iPhone and I have used regular digital camera (just like you), I have had professional photos taken and all in between.
I think the key to good pictures is not the camera (eat me alive photographers) but the composition and light.
Make sure you use light background so your items can pop up and that they are not weirdly cropped in thumbnail view.
For example, I personally think this is great:
https://www.etsy.com/listing/227989888/hand-shaped-brass-leaf-earrings-with?ref=shop_home_active_5the item really pops up and the colors of the background compliment it.
However, I would edit this one:
https://www.etsy.com/listing/227594572/faceted-watermelon-tourmaline-nugget?ref=shop_home_active_4because in thumbnail (how customers view the image when searching) it looks strange.
No need to invest in a new camera, I think...