@Arachnophoric about 3.5 inches, i'll be buying it from a seller saying that it is a female should I bought it? I saw a picture of it with a grayish bluish coloration, not like the males I saw on the internet that has a solid blue carapace, any ideas?
@John Ulrich males and females look exactly alike up until the male matures - that's when they get those deeper blues. At 3.5" males and females will not be visually different.
I'd ask the guy if it's been sexed by molt. Female M. balfouri aren't cheap. If he says it is, that's up to you to trust him. I'd also be asking on what will happen if it does indeed turn out male after you bought it as a confirmed female.