About 5-6 years ago, my hunting buddy shot a really small fawn and a couple weeks later shot a button buck.
At the time I remember thinking "Dang, I would have never shot that little bitty deer!"
Well, the following weekend, a lone doe comes walking in about 1 hour after daylight...she looks like a good doe to me and I haven't shot a deer yet this season, so I shoot, she goes down...I walk up to her and turns out its HIM. Little button buck. I felt like crap.
Well, I'll be damned if the EXACT same thing didn't happen to me AGAIN 2 weeks later. I went from never having shot a tiny fawn like that to shooting 2 over a 3 week period.
Since then, if I'm going to shoot a doe I TRY to always make sure she's with other deer so that I can compare them and then I try to take the biggest one. If I do shoot a lone doe, I always look at the face very hard. If they have a short, "cute" look to them, I don't shoot. A mature doe will have a long looking face and a long nose.