"I remember every wand I've ever sold, Mr. Potter." The use of the present perfect suggests that the speaker is currently still in the business of selling wands. Remember that the present perfect always tells you something about the situation at the present time. You asked ' Would it be correct if he said "I remember every wand I sold, Mr. Potter." or "I remember every wand I ever sold, Mr. Potter." ? ' Yes, it would be correct, but the use of the past simple would indicate that the speaker was no longer in the business of selling wands. We use the past simple for a finished or 'closed' period of time. For example, a retired owner of a magic equipment shop might look back on his former profession and say "I sold wands for 50 years, and I still remember every wand I ever sold." The adverb 'ever' simply means 'at any time'. You can use 'ever' in any tense - not just the present perfect. If the retired shopkeeper says 'I still remember every wand I ever sold', the word 'ever' means 'during my whole career as a shopkeeper'. This can be either an unfinished period (as in your original example) or a finished period ( as in the sentence above).

"I remember every wand I sold, Mr. Potter." is incorrect because 'ever' is implied here and to a native speaker it would sound strange. "I remember every wand I ever sold, Mr. Potter." is incorrect also. When you have 'ever' - it's generally a clue to use a Present Perfect tense. Sometimes you don't have these markers (other common ones are 'never, ever, just, already, yet), so you should think of it as something that happened in the past but is important at the time of speaking).