Start by being fair to the spreadsheet
Spreadsheets survive in sales teams for good reasons. They impose no structure until you want one, they can be changed in seconds, everybody already knows how to use them, and they cost nothing to start. For a single person managing a moderate number of opportunities, they are frequently the right answer, and arguments that ignore this tend not to persuade the people who would have to change.
The case for changing is not that spreadsheets are unprofessional. It is that they fail in five specific ways once more than one person depends on them, and that one of those failures is not fixable by any amount of care.