I will just throw things that I've seen on Classifieds that IMHO are good purchase - full disclaimer, I do not know any of these people. Brand new doesn't necessarily mean trouble free. Just remember to ALWAYS do transactions through PayPal and paying for product or service (NOT FAMILY AND FRIENDS), if someone wants a bank transfer - just avoid it.
At 250gbp, 2018 version ASG CZ Scorpion EVO3 allegedly used only 2 times, with 2 batteries, extra mags and accesories is in my opinion a steal - brand new gun with 1 mag and no extras (which are 20gbp each give or take) sells for 319gbp (and you need UKARA). 2020 version to my knowledge has just updated electronics (which can be purchased separately as an upgrade, would you so desire). EVO is considered one of best AEGs out of the box and is often appearing in recommendations for new and veteran players alike - it's a proven construction with long track record of reliability. It's quirk is a system implemented, that some either love or hate, that stops fire on empty mag and require pressing bolt catch release after loading new mag in to be able to shoot again. Great for that realism factor, bad for fast reloads if you're not used to it... also most seasoned airsoft players immediately assume their gun just broke when it stops firing
ASG CZ Scorpion EVO 3 A1 - Electric Rifles - Airsoft Forums UK (airsoft-forums.uk)
It's great at a distance, can fold stock to be even more compact for tight CQB action, it's lightweight due to it's polymer construction while not being fantasy gun (like G&G ARP9), it's one of the few airsoft replicas created in collaboration with manufacturer of the real firearm. As a matter of fact I have my very own 2nd hand EVO arriving today
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If you're into tacticool M4s, this is also a great RIF:
HERA ARMS CQR - Prefired
Comes with built in SSS mosfet that brings pre-cocking for that crisp semi-auto trigger response, spring release on switching fire selector to "safe" and gearbox diagnostics (so when gun shits the bed mid game you can have rough idea of what's the issue), can switch full auto to 3rd burst, has ICS signature split gearbox for easier maintenance and quick change spring - comes with HERA ARMS licensed furniture which is an acquired taste. Gambit’s Guide: How To Configure Your HERA ARMS CQR – RedWolf TV - YouTube