Purely a matter of staff/manager.

I bought the Thule Vertex 2 hitch mounted rack from REI. Through what I judge as weak design, I lost the anti-sway part, complete with its strap (it came off the rack while driving, this part swings from an axle, but there is no positive click when you hook it up, as a result, with no bike on and strapped to it, it can swing free and you lose it).

I asked REI if they had spares.

No.

I asked whether they could loan to me the part from a defective rack they have as a floor model (can't sell the rack, as the mechanism that holds it upright was broken) because in a week I was going off to a lengthy trip.

No

I asked whether they would order the missing part.

No, they only deal with complete racks.

Being the helpful sort (!) he offered that I should Google Thule and see if I could order it myself directly!

I did. Thule shipped the part which was delivered with 2 days to spare.