Hi. I want to buy this bike. Is it hydraulic?
If there are no signs of a metallic wire (often colored silver) exposed anywhere near either end of the black housing "tube" connecting the lever on the handlebars and the caliper on the fork, it means that it is a fully closed hydraulic line. Another giveaway for mechanical brakes is a moving arm at the caliper which visibly reacts when pressing a lever.
On your picture, the front brake we see is clearly hydraulic.