OBT 3" to 4" Molt

It's pretty easy, especially with larger tarantulas. Looking at the inside of the abdomen of the molt, locate the epigastric furrow and should there be nothing but the furrow (flat), it's probably a male. If there is anything at all looking like a little pink flap, a couple red pimple looking things, or really anything at all potruding from the molt between the first pair of book lungs then it's a female. Different species have different sperm receptacles (spermathecae) some are paired and look like little devil horns, some are as simple as a couple little red pimple looing dots spread out, some are like a little flap (OBT's have this type) and there are some others (and a couple T's don't even have spermathecae :? ). But anyway, hope that helped. Your pic is kind of blury so I'm not going to make any for sure guesses, but I'll say male. I see two little red dots but cannot tell if they are spermatheca or just dimples in the crunched up exo. See if your cam can focus a little better and we'll help you out much easier. I'm putting money on male though (females of this species have a triangular flap as adults, not a pair of bulbs anyway).

Thanks for the info. I'd say it probably male too. Only because of the probability of a sling becoming a male, AND it's kind of leggy.
The camera is a piece of crap though. That was the best pic I could take.

Don't worry I'm sure you'll find somebody with a female, everyone's got em. Hey why don't you buy a female? And also, being leggy is definitely a characteristic of male T's, but really only for mature male T's. Anything that is not mature, you can only truly sex by checking the molt or by viewing its underside. Now that I look at it that pic isn't that bad, a spider that big should have pretty noticeable spermathecae. Look for sperm bulbs on the pedipalps next