I get hassled every time I fly into San Jose Del Cabo. They X-ray ALL the incoming luggage before you get to customs so there is no denying what you're carrying. The customs form says you are allowed one still camera and one video camera and a certain number of rolls of film, even your typewriter and a microwave! When they ask me how many cameras I'm carrying I tell them one for stills, one for video and one for underwater. I always tell them I do this as a hobby and not a profession. This seems to be OK with that. They also seem to be more concerned about new cameras vs older ones.
You can also argue with the customs agents that you had no way of knowing what the limits were, since you were not given the customs form until after you got on the plane. I don't recommend this, but it has worked once or twice for me. Pleading ignorance usually gets you by if you tell them you have more than what is allowed before you hit the ALTO/PASE button. Just don't be short with them and don't lose your temper!
In other parts of Mexico, like Cozumel, I never get hassled. In my experience its easier for women to flirt their way through customs in Mexico than it is for men, with the exception of Cabo where there are more female customs agents than males. "I bring a lot of cameras because there are so many good looking men to take pictures of!" ... giggle ... giggle ... smile ... bat your eyelashes ... blush a little. Sorry guys, but it works.
Your best bet is to not take any chances and make a list of your camera gear with serial numbers, claim the extras on the customs form, and refuse to pay a customs fee because you have no intention of leaving any of the camera gear in Mexico. If you're working as a pro you probably already know that you can do the paperwork ahead of time to obtain a permit and avoid this entirely.
If you do lie about what you're carrying, you risk paying a fine, losing your gear, or spending a good hour trying to reason with the customs agents to let you go with your gear.
Just be sure that if you're bringing your psychotropic drugs that you also remember to bring your physician's prescription.