First of all, you should always make a purchase from reliable seedbank. Regular, autoflowering and feminized seeds, Sativa and Indica strains, finally – seeds slated for industrial hemp cultivation – all of them show almost no significant difference between each other, of course if we are talking about eye-sight. To be sure what you are buying, you have to rely on reputable source.
Did you know, that a single marijuana seed can have a size of a small pea or be as small as a tomato seed? This is not a manifestation of the future size (or health) of the plant which will evolve from it. You should also know, that most of the times Indica seeds are bigger from Sativa ones.