People often mistake the leaping salmon of Strathearn for the flame of Isle of Wight Studio, and if you don't know glass, you might think they could have come from a similar stable. Perthshire is related to Strathearn, obviously, so being unlike Strathearn, your seller must have assumed Perthshire.
It's no insult to either.

Colours are introduced using powdered enamels on the surface worked and marvered in. And IoWSG did copy the swirls of splodges of colours the Ysarts did.
There is a warning on Frank's Scotland's Glass not to confuse these.
Has it got the comet-like streaks of silvery deposits on the outside surface?
I used to display mine upside-down. The bottom was more attractive than the inside.