No problems selling. Just tell whoever buys them from you the params of your water and they will acclimate accordingly.
And yes, RCS have different grades. http://www.plantedtank.net/forums/sh...-cherries.html
The higher the grade the more they are worth. Upwards of about ~$5 each I believe (could be wrong here).
And I don't know about the UK, but Brita filters are cheaper if you drink a lot of water a day haha. Like somehwere about ~1g a day and you save quite a bit.