If it is fake it will most likely say Gucci on the belt buckle but if its real it will not and the stitching mite look a bit wavey or sloppey
Smell them.
If its under 100 dollars its fake, and all true Gucci watches have a dash mark under the G in Gucci. you can also tell because if the watch is gold or silver it is phony and if it is either pink,...
One hint is that they should be made in Italy. If you contact the actual manufacture they will often help you verify as well.
Fakes might have slightly darker color of brown on the side.