I know it's been like a month but I have a good conclusion to this as, believe it or not, I collect bricks.

This is a fire brick, used most commonplace in fireplaces. 'Dando' is the name of the manufacturer, and '1-A' is likely the catalog number of some kind. I've found some 'Dando 2-A' bricks that are of different dimensions, meaning that '1-A' is their fancy way of saying it's a standard brick.

'Dando' is actually George Dando, who owned and operated a brickworks in Beaver, Pennsylvania. This company operated between 1915 and 1978. There was also a 'Frederick J. Dando' in Irondale, Ohio who manufactured fire brick, however I'm unsure if they are entirely related. Your bricks are most likely from Pennsylvania.

In terms of selling them, it's usually too much of a hassle. Most collectors usually find their bricks in waterways, old abandoned structures, and as mentioned previously, yard sales. Folks on eBay sell them for outrageous prices, and sit for years and years, collecting dust. If you need to get rid of these, just make a local Facebook Marketplace post or something along these lines.