Maybe you wanted more than they are worth to that buyer ?
I see names that I would pay £90 to bb-online to try an catch, some I see I'd pay £42 (30+nom), others I would pay £35 regged in my name or inc reg fee, others I'd only pay £10 for.
So your domain you may have wanted £50 for but someone thought it was worth £30 so they want to buy it less and £6 means they can now sell for £30.
I have seen names in the bargain bin that I'd buy at reg fee but not £22, so if it drops I'll hand reg it.
I value every pound I make, lose, buy and sell, so see a difference, like I looked at STJs Fuel.co.uk name, he see's it as XX,XXX due to petrol/diesel but my use I see it more like early X,XXX because I have a use in mind and it wouldnt make XX,XXX, so I'll find another name. Same goes for your names