Chances are he got one from a rip off merchant, some stores have them at the 420 mark. Throw in the silencer etc. Still, nuts price, I've seem at 450 s/h but will have several mags, sling, rail covers and a mosfet
http://www.usedairsoft.co.uk/rif-s/electric-powered/new-vfc-cybergun-sig-sauer-mcx_i14973
Some crack being smoked here seeing as you can buy new for £380 in the UK, and sometimes for a lot less imported if there's a flash sale on Redwolf or Shootclub
I've had fast delivery before. Boneyard/special offers can be really good, worth checking. Bit slow to remove sold out items though, makes browsing clunky.
https://www.prefired.com/ads/rare-and-upgraded-gp-salient-arms-gbb-rifle-woc44/
Just because you spent a mint on upgrades doesn't mean this is worth 1.2k!