You can tell whether a Pokemon card is worth anything by working through four things, in order: what the card is, what era it was printed in, what condition it is in, and what buyers are genuinely paying for it right now. Do all four before you pay a grading company or accept the first offer a buyer sends you.
Work out exactly what card you have
Start with identification, not value. Look at the small symbol in the bottom corner of the card and check a few things against each other.
- A black circle means a common card, a black diamond means uncommon, a black star means rare, and a star marked PROMO means a promotional card, according to CGC's rarity symbol guide.
- The set number is printed as a fraction, such as 25 of 102. If the number on your card is higher than the set's stated total, CGC says that marks it as a secret rare, which is often the scarcer card in that set, as the same CGC guide explains.
- Check whether the foil sits only over the artwork, which CGC calls a standard holofoil, or covers the whole card outside the art box, which it calls a reverse holofoil, since these are treated as separate card types.
Check the era, and go careful on first edition claims
English language Wizards of the Coast cards were printed between 1999 and 2003, so anything genuinely from that run is an older card by definition, according to World of Collecting's breakdown. I would not try to tell a Shadowless card from an Unlimited one, or confirm a 1st Edition stamp, from memory or from a forum post. Check the stamp or print mark against an official reference, or let a grading company confirm it when you submit the card, rather than taking a seller's word for it. If your card happens to be a Base Set Charizard, I have written a separate guide on what affects that particular card's worth, here.
Judge the condition honestly
Condition decides more of the value than most people expect, and both big grading companies spell out exactly what they are checking for. PSA's own standards say a Gem Mint 10 needs four sharp corners, full original gloss, no staining, and centering within about 55/45 on the front and 75/25 on the back, while a Mint 9 is allowed only one minor flaw, such as a slight wax stain or a small printing mark, under PSA's grading standards. CGC grades on the same 1 to 10 scale, from Poor up to Pristine, checking centering, any manufacturing or handling defects, and signs of play, and says a Pristine 10 has to be flawless even under 10x magnification, under CGC's grading scale. Hold the card to the light and check every corner before you decide it is in great shape.
Is grading worth it from the UK?
Grading only makes financial sense if the card is genuinely scarce and in strong condition, because you are paying a submission fee and covering postage both ways, and sometimes customs charges, before you even get a verdict back. I do not have a current UK submission fee I can honestly quote you, so check PSA's own page and CGC's own page for their latest pricing and turnaround before you post anything. Turnaround time from the UK depends on which service tier you choose and how busy the grader is at that point, so check the current estimate on their site rather than relying on a number someone quotes you from a year or two ago. A common looking card in played condition is rarely worth the cost and the wait.
Get an actual price, not a guess
Once you know what the card is and roughly what state it is in, look at what buyers are genuinely paying for that exact card right now. A single eBay search will not tell you much, because the standard search for completed listings only shows the last 90 days, and you need eBay's own paid tool to see up to three years of that information, according to World of Collecting's explanation. I would scan the card and check a current figure with something like Collectly's value checker rather than guessing, and if you have more than a handful of cards it is worth tracking the whole lot in one place with a collection tracker so you are not rechecking the same cards every few weeks.
Selling in the UK, and the tax most people miss
If you decide to sell, know the tax position before you list anything. A personal possession such as a card collection only needs to be reported for Capital Gains Tax if it sells for more than £6,000, and if you own it jointly with someone else you are exempt on the first £6,000 of your own share, under GOV.UK's rule on personal possessions. That threshold is about the total you receive, not your profit, so keep a note of what you paid and what you sold for. Most single card sales sit well under that figure, but a well graded card or a full collection can tip over it more easily than you would think.
Spot a fake card or a scam seller
Counterfeit Pokemon cards exist, and the law is on your side if you get caught out by one. If you buy a fake, you are entitled to a full refund within 30 days of purchase, and the seller still has to refund you up to six months later if they cannot supply a genuine replacement, under Citizens Advice's guidance on fake goods. If you suspect a seller is dealing in counterfeit cards, you can report them to the Citizens Advice Consumer Service, which passes that information on to Trading Standards, under the same guidance. When I ran my shop, the fakes that caught people out were almost always the ones nobody had checked under good light before paying.