I don't want to be that guy, but you can get these brand new for £94.95 from Airsoft World.
https://www.airsoftworld.net/we-glock-g17-gen-3-tactical-gbb-airsoft-pistol.html
The price you've asked for the gun is fair I would say but it's the carriage charge that makes buying it from you redundant.
Most folks would probably rather buy a brand new one.
It could be worth looking into lowering your postage costs.