To get an idea of where this logo will be used, please take a look at the attached file for a draft of my blog.
A good logo is unique and memorable. It should express something about the company it represents. It should take into account the technical considerations and the feel for the site. A good logo should express a strong message.
The symbolism should be immediately clear, without it being too clichéd. For example, a auction hammer or a stethoscope in the logo wouldn't look very professional.
The logo should look friendly, and something that is memorable and will create an online brand.
The logo would need to work on most colored backgrounds in case I ever redesign my blog in the future (please see the attached file for a draft of my blog).
When thinking along the lines of health, nothing should relate to failed health (pills, doctors, etc) and only good health (exercise, walking, bicycles, muscles, etc) should be considered.
Along the lines of auctions, using eBay colors might be a plus.