Skip the big-box stores
The 'Good' version features only a small increase in the number of rare cards so that you can get started making tweaks right away without needing to buy any expensive cards
It's possible for a card to be banned in Modern that's unbanned in Standard, though that doesn't describe any cards right now
To avoid these complications, many UK collectors use a domestic PSA submission intermediary services like Cardhawk, for example, which accept your cards in the UK, handle the overseas logistics on your behalf, and return your graded slabs without the customs headache
There are two exceptions to this, specific Shiny cards which are earned in different ways: Shiny Mewtwo ex: A promo card and part of the Paid Poke Gold Package in the shop
The rule for setting the MTG cards value is quite simple: "The more players like the card and buy it, the more valuable it is." But this rule does not work with all items