bmac56 - I think some of the questions you asked have been addressed either in this thread or the original one posted a while back. I might be able to help you out with a few answers/opinions though.
1) They set the max of 50% off asking price for offers because people were being bombarded with ridiculous lowball offers constantly. I think they had enough complaints about it and found that it would be a good idea, which I like.
2) While a trade option would be nice, I think it would be a programming nightmare to add a trade/trade & cash option. It is very doable, but writing the code for it would/will take some time. Not sure how it would effect the inventory management, as I have no clue how that works. But I am sure it would create additional steps in the process requiring more people and/or time.
3) There are better alternatives for base cards. As Mike pointed out, sportlots is about as good as it gets for set fillers. Most of the cards you can pick up for about $.18 each and reasonable shipping. Also, doesn't hurt to post set needs on the forum here. Lots of guys are more than willing to help people out with filling in sets for little to no cost.
Hope that helps a little.
Looking for - Jose Osuna, Clay Holmes, Alex Dickerson, Luis Heredia, Josh Bell, and Gerrit Cole