I recommend sticking with the blue and orange colors used with the mockup logo that is shown in the screenshot, you can also use any other color but its important that it fits well with the existing website mockup.
The winning design will need to have 2 versions to it:
Web Version - 2-3 color logo that can use gradients.
Print Version - 2-3 solid color logo that can be used for printing.
Also need a icon for the address bar in the website
The logo can incorporate auction elements such as an auction hammer or something else, but it doesn't have to at all. Just be creative and show me what you create! Must be fun and should be attractive