Well here's my reasoning:
this is my own personal belief but I recall some members on the forums sharing the same opinion... I REFUSE to believe that someone who claims that a gun that is upgraded to the teets is "lnib never gamed". Why did you upgrade the internals for performance if it's never gamed?
What I mean to say is that your guns are presumably LNIB never gamed. The internals and externals are in stock pristine condition if not a little dry on the insides due to a lack of cycling or lubrication.
The offering party is proposing a gun that's upgraded and PRESUMABLY gamed at least once if not more.
Why would you trade a perfectly new gun that doesn't even have a scratch for one that's of lower-quality, prone to breaking (and all stock glock plastic frames have this problem whether it be black or tinted, it all depends on the owner and the use of the gun along with age) based on the length of ownership, and it doesn't come with mags?
The PGC slide set is $90 in-country at best and requires modification and fitment for proper use according to this thread:
TM Glock 17 Metal Slide + Outer Barrel (PGC or Guarder?) - Airsoft Canada
The remainder of the upgrades:
HK3P G17 ($150 presumably used, $220 new but it's discontinued based on Depot prices)
PGC Slide Barrel Set ($90 based on Parts)
Guarder Steel Night Sights ($30 China retailer)
Guarder Magazine Catch ($10 based on Parts)
Guarder Serial Plate (lolwut)
Maple Leaf Hop Up Unit ($30 based on Parts)
Maple Leaf Enhanced Hop Up Wheel (i donno what that is)
Maple Leaf Hop Up Rubber ($10 based on Parts)
Precision 6.03mm inner Barrel (unkown brand) ($20 presumably based on China)
Total approx $410~ MSRP
Total approx $340~ MSRP - used price on the G17 alone
Considering what we know about the fitment of the slide and that it's almost definitely probably without a shadow of a doubt used, we can probably slash that price in half given the "nature of airsoft". Ask yourself, do you know this owner and how well they've maintained their gun?
$160 without mags for a used hk3p G17. $200 is a reasonable price for that specific hk3p imo. Throw some mags you've got a decent deal for $300 cash.
I've sold a WE G19 for $120 with no mags and the only upgrades were springs and glow-in-the-dark sights.
Your VFC Saber MSRP is a whopping $500 CAD after taxes in-country. Up to you though. Feel free to disagree with anything I wrote.