I imagine they'll actually sell quite well. This website isn't a brilliant snapshot of the "market" for these scarves. We're all big enough Rovers fans that we go out of our way to spend time chatting inane shit about them online. We're not going to buy something with any other team's badge on it.
There will, however, be a lot of Celtic supporters who see the Rovers as their "wee team", or even vice versa. Again, if they were to pop up and say such a thing on this website, they'd be slaughtered. But you know there are equivalent folk in your workplace/primary school class. There'll also be a few a lot of folk who come along to this game and it'll be their first Rovers game, or the only one they've been to in years. Chance might be they fancy a wee reminder.
The bottom line is, like it or not, there's a market for this product. It's no worse (in fact, it's a damn sight better) than SPL clubs giving over "home" areas to Celtic (and formerly, Rangers) fans to boost their gate receipts. It's the world we live in. Until there's a fairer distribution of wealth, Scottish clubs have no choice but to "flash their gash" at the Old Firm.
Morals are all very good, but they don't pay the bills. It's a half-and-half scarf, it's not like we're agreeing to play the game without a goalie in exchange for £50 and some old training cones.