To answer your question more completely, SSDI (which is what I am on) is not so picky as to what other income you bring in the way SSI is (kinda like welfare for disabled people). From what my worker told me, I can receive up to 1000.00 of income extra per month in addition to my SSDI checks. (I know info from SSDI is not always right on..so don't take my word for it). I have 9 months to actually make as much as I want to, in order to see if going back to work and dropping SSDI may work for me. In my case I can't work period, but it's nice to know this info. She also told me after 9 months, they would deduct anything over 1000.00 per month from my SSDI checks.
From what I hear, it's possible SS may perform an early review of your illness/handicap if they see you are working excessively and no longer need SSDI income. I do know many on SSDI that work only 10-20 hours a week at home, or at a brick and mortar that have for years with little to no issues at review time. I used to work from home when I lived in Florida, and met many people online who were on SSDI. In my honest opinion (off the record) selling the scant item online for a couple hundred extra per month won't bring you any notice. And no, they can't see your bank activity. However, you should probably make it a point to find out how and when to report the extra income.
You will want to call SSecurity up directly to confirm this..