I've definitely had those moments a few times...usually based entirely on the way the toy looks and a quick glance at the overall vroom/bee rating.
But I generally take time to read the reviews before I toss it in the cart...it's easier to avoid disappointment that way. =3
For me it's usually bold colors (usually shades of blue or pink) that catch my eye or things with glitter on them. I've always been a sucker for pretty colors and glitter. u_u;