Hi Richie,
Just being honest with you, £250 is a bit much. Paintball markers are a bit like new cars, as soon as you drive them out the showroom they drop in value loads.
As £210 +P&P is the new price you should be looking to sell your A5 for around 25% less than that, or £150-£160 +P&P
Yes you have got a sniper barrel, but assuming it is the Tippamann one, it's not really worth anything as it is the same as the standard barrel but a bit longer (if you had a flatline it would be a different matter).
I am not trying to piss you off, just letting you know what you can realistically expect.
Regards Alex