Some companies aren't so tough - Chris Webb from Biomechanical is endorsed to/by PRS, they even did a custom 7 string for him. As far as I'm aware, there's no requirements to do with minimum number of live dates/CDs sold/number of magazine appearances. Bass player from same band endorsed to/by Warwick and both guitarists Framus amps. Again, I'm not aware of any requirements for those deals beyond the usual 'must use live and in studio shots' type of thing. The Framus deal, I've been told, is that artists pay £1 for each item for it to be theirs (probably something to do with creative accounting with taxes and expenses!!) and can basically choose whatever they want.
The band also have a deal with Jagermeister... *burp*!