Had a recent service issue with Allegiant on an EUG-OAK flight. They subbed an Airbus in for the regularly scheduled MD-80, with the result that seat assignments then were confused--some people, it seemed, were assigned to the same seats, or who knows. By the time I boarded, the FAs were directing people to take any open seat. Not a problem, except they weren't providing refunds for the seat reservation fee for quite a few people who weren't getting what they'd paid for.
At OAK, I talked with one of the Allegiant contract staff, who was friendly and helpful, and made some notation in my record. I followed it up with an email to Allegiant (since good luck contacting them otherwise), and after a couple weeks they sent me an apologetic email and refunded my $14 seat fee. Acceptable, at the end of the day.
I suspect that this kind of thing will occur with greater frequency as Allegiant increases the numbers of Airbuses in its fleet and swaps with MD-80s become more frequent. It will lead me to simply take my chances with check-in seat assignments, rather than paying money I might have to hope will be refunded if there's a swap.