there are 3 types of puffer that can be called green spotted.
Tetraodon nigroviridis
4-6 inches.
usually only get to about 4 ish in aquariums.
and they are brackish not freshwater
Tetraodon fluviatilis
5-8 inches, fresh when young and moving to brackish as they get older
Tetradon schoutedeni
4-6 inches, a true freshwater puffer but rare to find.
you fish shop, may well sell you one as the wrong species, so what you should do is go to the shop armed with your own information and make your own decision about what they are (or take someone who knows!!)