Limit who has the say in purchasing. As for the free goodies (hats screwdrivers etc, under about $20) don't worry about that too much. If guys are starting to go on vacations or getting large gifts, that is a problem.
Have a chat with the salesman and say what the limit is, and if they want to give out larger gifts (jackets, large gift certificates...) hold on to them and do a draw for them at a company outing (golf, bbq...). This way it helps keep everybody objective.
On all equipment there are 2 levers...
Lever "A", and Lever F'in "B"