Buying tuned s/h air rifle only to 'fix it' by putting back in factory parts

[rapidresponse1]

i bought a lovely tuned 95 off a gun smith best spring gun ive owned

[rancidtom]

Obviously it is down to the buyer, do you the buyer believe the seller? Has the seller any proof who tuned the gun? Can you try the gun? Does the seller have a chrono?
When I tune a gun I give the customer a chrono sheet, sometimes a test target to prove grouping at a decent range (45 yards) if they have asked for this (and can pay for the time taken to do this). My tuned guns have warranty numbers and tamper evident seals which are individually numbered. If a potential customer wishes the enquire if I did tune a gun I will firstly search my records for the serial number, if I cannot find it I will make the customer aware it has never been through my hands, if it is in my records then I will be able to tell the customer when I tuned it, what I did to it, who I tuned it for (as it may well have changed hands since being tuned). All this is good information for a potential sale or gives the customer enough information to walk away before being "stitched" with a gun that either I have never laid eyes on or has been messed with since I did if the tamper evident seals are removed or broken.
A reputable tuner (or at least one who wants to preserve a reputation) should be able to do similar for a customer, even if the new potential owner hasn't ever had any work done by me s/he will be able to benefit from sending the gun to me in the future if it needs a service.
Just because a gun has a sticker on it doesn't mean it's been tuned by the shop/tuner concerned, but if the sticker is a warranty number that might imply the tuner could confirm what the seller claims.