It is a big deal especially when it took me 60 seconds to pay for it over the phone and it's gonna take 24-72 hours to get a refund so I can order one elsewhere. If I had to wait 4 months for a car part in these competitive internet days, I'd do without.
I'm not shopping around for the best deal, just to save a couple of bucks. I just want my part in a reasonable amount of time. If I'm told it's on backorder upfront, I will not deal with that vendor.
When a part is on backorder, they have no idea of when the part will be available. The time frame they give you is just a date they hope they can get one by.
I usually ask about availability, but since they called their source before I ordered, I took it for granted they had one in stock,