I try to send extra of the same cross if I have it as a bonus that way they have extra if something happens to one or two of them. I do also send other crosses as well of only 2-3 seeds if I don't have extra of same cross. I usually try and sort my seeds in equal amounts with the bonus number included. For example if I have sorted out 15 seeds I will then list it as 10 and the extra 5 are bonus. This number isn't exact but you get the idea.
Not that I'm too picky but a lot of the bonus seeds I got when I purchased tons of seeds in fall 2010 I wouldn't have chosen for myself and would have rather had extra of the ones I bought. Most of the bonus seeds got tossed as seedlings when I was having to pick and choose what to plant when I had to move because of the space. Now if it was something I actually purchased and wanted I would have made room