I'll be honest with you. I have never had a man other than my husband buy me a drink. I always wanted to know what it felt like to be found attractive and have a drink sent over my way just for the experience. There are several reasons why this hasn't happened to me. I got married at 18 (years before I could even go into a club or bar). When I was able to go into a club I was escorted by my husband.
Now if I go alone with friends, I decided I wouldn't accept a drink from a stranger because 1) I don't want him expecting something in return for it 2) I don't know if he drugged it 3) I don't feel comfortable with a man buying me something that could ultimately effect my ability to consent.
So men, if a lady doesn't accept the drink, might consider several of the above reasons.