There is no "safe" way to pay, once the money goes out of your bank account that's it, and PayPal will not cover anything gun related, so you have no redress from them. If your worried - don't do it, or have a day out/night away with the Mrs and drop in and collect in person, I've done that a few times over the years
You can only do so much to mitigate problems, but remember, being a pistol it can be posted RM 1st class recorded and covered for it's value, it wont stop a scam, but it should not be an issue getting lost in the post if done properly.
Alternatively, if there is a forum member close by who is willing to act as a go between? just an option, there are plenty of people on here I would trust rather than a stranger
Good luck.
James