When I share oranges with my wife, I take two oranges and cut them in half. I give her half of one orange and half of the another. This is because I want her to have at least half of a good orange. It's also so I don't end up with a full bad orange.
Fundamentally, I've managed my citrus risk through typical strategies; including transferring the risk to another party, reducing the negative effect of the risk, or accepting some part of the risk.
There are many risks that could affect your online business: eBay recently introduced Detailed Seller Ratings (DSR), which may reduce the visibility of high-volume sellers; search engines could change their algorithm to reduce the number of customers who find you; or your prime competitor may continually outbid you on an effective Comparison Shopping Engine (CSE).
A high-volume eBay business could experience some volatility when eBay adds features or changes policies. Detailed Seller Ratings, changes in search results, Trust and Safety programs, and shipping edicts may all affect your business. By increasing or improving your sales channels, you limit the risk to your business overall.
The first and most important step is creating an online retail presence and driving traffic to that site. After that there are multiple marketplaces, including Amazon and uBid, comparison shopping engines, and search engine marketing tactics. All of these are ways of diversifying your sales channels and managing your online business risks.