No dedicated GPU on 15" 2017 Macbook Pro?

If it is a MacBook Pro14,3 it should have one, so something is wrong. Confirm the model identifier. The pawn shop may not be ideally qualified to determine it.

Try (Apple menu) > About This Mac > System Report... > Hardware > Graphics / Displays. Take a photograph and post it in a reply.

The model identifier can be found in Hardware Overview.

It does not have a dedicated GPU. It may have been an option for the top-end model. The model you are looking at only has integrated graphics with shared memory.

Discrete graphics was not an option in that model--it was standard equipment. Here is the the original Apple spec sheet for that model:

MacBook Pro (15-inch, 2017) - Technical Specifications

The MacTracker database and everymac.com both also list that model as having both integrated and discrete graphics: the Intel HD graphics 630 integrated, and either a Radeon 555 (2GB VRAM) or Radeon 560 (4GB VRAM) discrete chipset.

It is possible the Radeon has failed and a previous owner has used software to disable it.

Was the computer running on battery at the time of the screenshot? Normally the integrated graphics run when on battery power to give longer battery runtime.

To make sure, examine the same "About this Mac..." page with the computer on wall power with the power adapter. If the Radeon chipset does not appear on wall power, walk away from the deal. Fixing a dead discrete gfx chipset requires a new logic board that would add $700-1000 to the cost of what started as a "bargain."

Used/abused Apple products from unknown vendors are common causes of "What can I do now??!" posts here. Save yourself the grief and expense is in doubt.