B757-200 CAPT RPTS PARKING MARSHALLER WAS INATTENTIVE TO CATERING TRUCKS THAT IMPINGED THE ACFT'S PATH TO THE GATE.

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DURING TAXI IN TO GATE; OUR GND CREW BEGAN TO GIVE ME HAND SIGNALS WITH LIGHTED WANDS TO PROCEED IN ON THE LEAD-IN LINE. THIS REQUIRES A 90 DEG TURN TO THE R. DURING THE TURN; I STOPPED THE ACFT AS THERE WERE 2 CATERING TRUCKS OFF TO THE L SIDE AND I WAS NOT SURE THAT I WOULD CLR THEM WITH THE L WING. I FLASHED ALL OF MY LNDG AND TAXI LIGHTS AT THE GUIDE MAN; WHO APPARENTLY DID NOT THINK THERE WAS ANY PROB; CONTINUED TO GIVE ME THE COME FORWARD SIGNAL. I REFUSED TO MOVE AND FLASHED THE LIGHTS AGAIN AT HIM. A SECOND GUIDE MAN CAME OUT AND TOLD THE DRIVERS OF THE CATERING TRUCKS TO MOVE OUT OF THE WAY. ONLY WHEN I FELT IT WAS CLR AND WAS ALSO RECEIVING HAND SIGNALS FROM THE GUIDE MAN; DID I MOVE FORWARD TO THE FINAL PARKING STOP POS. GND CREWS NEED TO BE REMINDED THAT THEY NEED TO VISUALLY CLR THE RAMP BEFORE GIVING THE SIGNAL TO ADVANCE ON THE LINE. GND CREWS ARE GETTING VERY SLOPPY IN THEIR PROCS. IF I HAD BLINDLY FOLLOWED THIS GUY'S SIGNALS; I WOULD HAVE HIT THE CATERING TRUCK WITH THE L WING CAUSING MANY PROBS.