Una sonrisa cautivadora would probably translate as a captivating smile or maybe a seductive smile.
When you use una sonrisa compradora, could that be used to describe for example a salesperson who smiles to try to instill confidence and good will in a prospective buyer and gain rapport with them? You might try a winning smile or a confident smile but your best bet might be a persuasive smile.
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If you find something wrong with my Spanish, please correct it!
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