That those whom the informers alert to Samson’s presence are called Gazites
suggests that the informers were not Gazites themselves, but people from outside the city, or even resident aliens, like David and his men were (in Gath) at a later time (1 Samuel 27:1–12). Whatever their identity, these informants must have felt that it was in their interests to side with the Gazites against Samson, and effectively handed him over to his enemies as the men of Judah had done. The men of Judah did it openly, by binding Samson. These do it secretly, by telling the Gazites of his whereabouts.
1
On the other hand, there is the possibility that if, before Samson went in to
the prostitute his presence was unknown to anyone else, it is the prostitute who would have been the source of the information. In that case we would again be faced with the picture of Samson being betrayed by a Philistine woman.2
2 The Gazites were told, “Samson has come here.” And they surrounded the place and set an ambush for him all night at the gate of the city. They kept quiet all night, saying, “Let us wait till the light of the morning; then we will kill him.”