Many cards now have a much higher card capacity and purchase cost than before and the increase in Deck capacity has been drastically reduced the player only receives a paltry increase in 1 capacity when defeating a Duelist that can be challenged repeatedly and 3 for any Duelist that will only duel once
not drawing the most important cards, never getting some way to easily add them to the hand, or straight-up bricking (a term which means that you have no way to play any card in your hand at that moment, therefore youre stuck)
A PSA submission runs roughly $20$150+ per card plus shipping and insurance, and the value usually needs to be ~34 the raw price to make sense
In general, any eBay seller with 10,000s or 100,000s of feedback is probably safe
Finally, one last aspect of the system I want to cover is the actual scanning process