Help with AquaFX RODI Unit

[Jaws]

Hey guys. I found a good deal on a very slightly used AquaFX RODI unit that someone locally is selling. They're advertising that it's 300GPD and based on the pictures it's this unit right here:

http://www.aquariumwaterfilters.com/...emart&Itemid=1

The thing I'm worried about is this unit can also be as low as 50GPD but you can pay extra to make it a 300GPD filter based on that link. The person selling it doesn't know where to look to make sure it's a 300GPD unit and I was hoping someone here might be able to tell me where I can look to confirm it. Thanks in advance