It really depends on your market; if people have money for flowers they will buy them... We used to do a very large market in a wealthy university town and there were 4 or 5 large flower sellers that seemed to do brisk business. Compare that to our
local market in a small, economically depressed, town; we tried to sell flowers but people were much more interested in bargain hunting for cucumbers and
tomatoes. We would inevitably end up cutting the price by half or 3/4 and still taking them home with us. You just have to know your market I guess...
All that said, you don't have too much to lose. Flowers are pretty easy to grow and beautiful to see in the garden, even if no one is buying them. Plus you generally don't have the extra labor in cleaning and packaging as much as say, lettuce or the like.