I don't think new managers should be able to make bids (or maybe just higher bids) on players for their first few weeks or so.
There probably should be some sort of notification in the bid process where if a new user bids on a guy with a high salary or old and high potential that there's a message that says "Hey, stupid, are you sure you want to do this?" Not in those terms, of course, but at least giving them some sort of warning and making them affirmatively choose to make their mistakes.