Definitely echo the above. If a RIF is available in the UK I'll tend to get it here (granted there's still many occasions where a gun I want isn't available here) as I've found they often worked out to literally cost about a fiver more from LWA/PAS/AZ even if you had the value marked right down. Also returning guns would be really expensive and a massive PITA if they went wrong. I've also had some extreme wait times with customs on a couple of occasions when importing RIFs. Generally it's fine and I always got all my stuff in the end, but if you get a proper jobsworth assessing the parcel who doesn't understand the law and/or your player number isn't written in f*ckin massive letters on the box, they go in to this whole process of snail-mailing you forms to fill in regarding your VCRA defence and the values of the package. It only really happened when I brought in a mahoosive box with 2 AR Carbines inside which drew massive attention - genuinely the smaller the box is the less they care about it it seems (or so I've gathered from importing a lot over the years).
I almost never find the little bits and accessories/parts I want over here though, so I'll save up a bit, do a good amount of digging around between WGC, eHobby, UNco, echigoya, Tokyo model, Airsoft Global etc to see which one/s will give the best deal after everything's taken to account. Generally wait until something's at a really good sale price and bring in quite a few bits in one bulk order; far more efficient postage cost wise that way.
Specifically regarding WGC, they've been my go-to for a long time now, I've built up quite the loyalty discount over the past 7 years or so. One time they sent me 762 Magpuls instead of 556 but that was the only mistake they ever made with an order and I've bought from them dozens of times. They sorted the issue out very quickly and got me the right items without even returning the wrong ones; though I do personally have a practice of physically filming myself cutting open the box and slowly taking everything out, just to be on the safe side. As I say, only needed it once, but it's super easy to do and provides irrefutable evidence to the shop,