Look at it this way, what are your interests / hobbies?
Is there something you like to do and have some knowledge of?
Knitting, cycling, running, speaking, pet grooming, office work, labourer?
Focus on that first, survey the market and see what is currently being advertised in that area and if it matches your interest/s and you see others are selling, perhaps target that?
I eventually plan to branch out and sell more than just consumer electronics, but I am sticking to something I am familiar with and can provide answers on if someone asks me about them (so far so good on the answer front).
That's my 2cents.