I find it odd that the retailer would communicate your vehicle make/model to his supplier, and that a supplier would scrutinize his customers order.
When I order anything from my suppliers, I tell them I want part #xxxx, quantity XX, purchase order XXXX, shipping details and thats about the length of the discussion. The burden is on me to ensure I ordered whatever correctly.
Likewise when my customers order from me, they specify part # xxxx, quantity XX, purchase order xx, ship here. The burden is on them to order from me correctly.
Not saying bait & switch but the vagueness of "bad fit" and eagerness to have you pick something else.... maybe try another Niche dealer. If Niche bawks twice, well there you go.
I think the wheels will look great. 10 wide would be my only concern. What size tire did you have in mind?