Rev wrote- Princess's wine tasting, usually held on the first day at sea, is a very good deal -- you pay $5 for the tasting but receive a credit of $5 if you order a bottle of wine at the tasting to have with dinner in the dining room. The wine that you order at the tasting can be any wine on the wine list, and does not have to be one of the wines sampled at the tasting.
I guess it has been a while since Rev has sailed with Princess. The wine tasting is now $9.50 and you do NOT get anything back if you buy a bottle of wine. They also have a tasting of much better wines for $25 per person.