I’d probably do the same. But, whatever you decide, try to buy it in a nearby store (to calm down paranoia of messing with the hardware by the seller) and bring 2 usb sticks with you: one with Qubes 4.1 iso and the 2nd empty to which you would insist to try the hardware and install Qubes on that other stick.
You may then try to check if IOMMU is enabled at the spot.
For ordering online, I’d arrange “return-if-qubes-not-working” policy.
This is only how I’d do it, exclusively personal “how-to-buy” guide.