Educated guesswork i think:
Evaluate the amount of V-RAM you need on minimal settings, don’t recommend a GPU with lower capacity.
Benchmark your game with precise render and update timings. Guess what kind of CPU and GPU might still be able to run your game.
Idealy find a PC/Laptop with similar or worse specs than your recommendation. See if your game runs and how well. Adjust your recommendation accordingly.
Your Players might try to play your game regardless of if they meet the min specs. At least I did, when i just had low powered laptop.