I cannot stress that too strongly. You will likely be buying an instrument that is 60 or more years old. Retuning a concertina is a specialist job, and expensive to boot. If you are seriously considering a particular concertina don't be afraid to ask the dealer to take the ends off and let you look inside. After all, you may find anything up to and including woodworm.
Old concertinas come with steel reeds most commonly, or brass reeds.
The leading name in anglos was Jeffries. Again Lachenal also made a wide range of instruments. Crabb also made many fine instruments, as did Wheatstone with their Linota range. With concertinas, you get what you pay for. There are few bargains around, but you have the consolation that if you have an instrument of reasonable quality or better it will hold its value and you will have no trouble selling it if you decide it is not for you.