Not to be discouraging, but it tends to be hard to overthrow an established site. Chat doesn't strike me as a useful feature for a sales site, and awards and badges only have meaning (to me at least) if they somehow relate to the reliability of buyers and sellers. Prettier (and more modern) interface would be great, but isn't going to be enough to get people to switch.
I have two AquaBid usage patterns:
1. I want something. I go there, look for whatever it is (it's usually quite specific) and buy if it's there for a reasonable price. While the AquaBid UI is fairly awful it gets the job done.
2. I want to learn about different options available in a category. I browse the categories and open items when I don't know what they are or want to know more about them.
A couple ideas for things that could be useful:
1. A better search feature with more advanced search options, ability to search specific fields, ability to do some boolean queries.
2. More fields in the description of the items. (e.g. A specific field for the species name, and separate fields for the common names.) This ties in with #1.
3. In the listing of items in a category or search results show thumbnail photos, and if one hovers over a photo, show additional detail - it's nice to not have to click away from the list unless the item really is interesting.
4. Better features for quantity selling. E.g. A seller has N fish of a particular type available, and is willing to sell them in any quantity (1-N). Allow the seller to specify this for the listing, and then automatically keep track and update the listing as buyers buy some of the fish. For instance, if the person has 10 fish, and someone buys 4, now the listing should say there are 6. And so on, until they're all gone.
5. Related to #4, allow the seller to specify flexible pricing based on quantity purchased. For instance, < 5, $5 each, >=5, $4 each, etc....
My suspicion is that it will take a fair number of little detail-oriented things like the above to actually get people to switch (as opposed to better performance or UI).