This is hazy ground.
It depends firstly on what level editor you used to make the bsp. Many (such as the standard Halflife and Unreal ones) need you to pay a liscence if you are commercially using them - this is usually far from obvious just by downloading and running the seemingly "free" software
One of the best BSP editors is Quarke. It claims to be 100% royalty free, which I believe it is BUT you have to choose a game format to use, Quake 1,2,3, Unreal, Halflife, Rtcw etc. I believe that if you use any of these standards to make a level you may well have to pay a liscencing fee if you sell more than x ammount of software

(
Good news? Umm well Cartography Shop is easy and uses no external game engine, and comes with files to convert its format to .bsp - so I GUESS thats completely air tight. - But don't quote me

Plus bad news is its not the worlds most flexible tool and you have to pay 4 it

Its pretty good tho, and intergrates well with dbp