I have sent well over 150 RIFs with parcel force and only ever had one damaged - probably my fault for poor packaging. The basic cover is £150, and that applies. You can get enhanced cover on the accessories, so actually with your price attribute the rest of the value to the hard casse, mags, etc, and you would reach a full amount, but you would push the postage cost up over £20. They are super reliable, it is so well tracked that it’s almost impossible for correctly addressed and labelled items to go missing
**** Not a question as such, but just to help you a bit, postage with Parcel Force 48, which is the only service you can use to post this in the UK, will only cost you £12ish, can’t remember actually if it’s £11.40, or £12.20, but it’s no more than that. Booked online, using the drop off at the post office option. And don’t take the enhanced comp cover as it does not cover Airsoft RIFS
Are you aware that you can buy this gun for £250 at retail with warranty and its rubber filter intact?
https://www.justbbguns.co.uk/sr36c-dual-power-gbb-line-airsoft-gun-with-gas-mag/
May I suggest you use the Appraisals page so you can come up with a more competitive price?
https://airsoft-forums.uk/forum/151-appraisals/