Just received a G1 devastator and not 100% sure if its a real G1 or a KO. The colour is spot on with a original I have back when I was a kid, however my stamp has Hasbro Takara and these have only Takara.
Is there any way to tell the difference, before I blast the seller?
You have nothing to worry about. The KO's only have Hasbro stamped on each toy. Below are some comparison pics for you (the ones on the right are the KO's).