If you guys are really worried about day trading I have mentioned this ten times before it can be stopped in a second by simply giving all new players a team buys from the TL a "guaranteed" contract of X weeks. Until X weeks is up the player cannot be listed for sale, sold or sacked. Simple.
For the value of X I suggest two but four would be even stricter and not unreasonable. One tactic that I think is very fair is a lot of trainers who do one position training will buy 2-3 extra players when they do skills that require two positions, like rebounds, then at the end of the training period sell those guys at a big profit. I think this is perfectly fair and good and four weeks wouldn't lock them in for too long.
Note: Players on a newly created team or draft picks haven't signed any contract yet so they can be sold, sacked at will, thisrule is only for players that are bought, so that they cannot be bought one day and relisted the next for an intended profit.
This isn't to say that I haven't heard of players reporting to a team and being sent home straight away. This used to happen all the time in the Aussie NBL back in the 90s. There was a phenomon called "Pacific Shrink". A team would sign a 6'10" C straight out of college in the USA, then when the player arrived he would really be 6'7". There was even a player who turned up and couldn't walk and hadn't mentioned he would be out injured for the next three months. hese guys got sent right back home, but I guarantee the recruiting tea didn't get rich off these guys.