As someone who has a seller store one of the constant questions I am asked by friends and other Ebay sellers is why I don't branch out and sell other items besides clothing, shoes, accessories, and jewelry. Though I have sold the occasional vinyl record and band poster I really believe that one of the reasons I am most successful is because this is my niche. Consider walking into a consignment store or boutique, how would you feel if this store was also selling teapots, DVR players, car parts, and lightbulbs? You probably wouldn't stay too long and find yourself going somewhere else, especially if you're looking at a high end item. My followers (and repeat customers) know that when they look at my shop it will always be within the fashion industry. My niche is clothing, and I do my best for it all to be fashionable and wearable. What I mean by wearable is something that can be promptly worn (as all my items are washed/drycleaned) or repaired to be worn quickly. I try to make my shop be like an actual store so that buyers are comfortable purchasing an item from me that is $16.99 or $369.99.
I must emphasize that this is my business model, and doesn't necessarily need to be yours. I have purchased many incredible items from sellers who are literally selling Ikea furniture bolts and souvenir shot glasses in the next listings. There is no wrong answer on Ebay as long as you're being honest with your listings.