How should I give thanks after a success

Thanks after a good reading is a small closing, not a second reading. Three traditional forms:

Thank the cards themselves. RWS practice treats the spread as a loan — the reading is finished, the cards are put away face-down or gathered back into the deck, and you say plainly what the cards did for you. "That landed, thank you." Nothing needs to be earned back.

Thank the querent's part in it. A spread only sharpens what was already half-formed. Naming the thing you did — asked the question plainly, wrote down the answer, went and checked the document — is the usual form of that thanks. It also keeps next week's reading honest, because you know what actually got you the information.

Record it. The most concrete thanks most people give is the journal entry: the question, the cards, and what you did about it. That's the practice's own record of what came back, and it makes the next spread sharper than this one.

One thing worth saying plainly: tarot reading is not a spell that produces an effect you then owe something for. If by "spell" you meant a ritual you did in another tradition, tell me which one — the way you close and give thanks in that craft is different, and I'd rather not describe it from guesswork.