@Drek Correct. Juvenile males and females look the same. The males don't develop their leggy build until they mature. (And when males do mature, it's far better to check the palps for emboli, which all mature males have.)
@Drek Yeah, pretty much, immature males and females are practically identical, some species are also naturally leggy (long front legs are standard for Lasiodora species) so you can't use that to tell them apart (for example, my G. iheringi female is all legs). You either need to wait for a moult and check it for spermathecae (if you Google "Lasiodora difficilis spermathecae" then you should get image results that show you what to look for) or you can post a photo similar to the one in my earlier comment and people can guess the sex for you.
So my dear lasiodora brought its moult outside of its burrow and I took a photo of what seemed to be the underside of its abdomen. I don't know. Can anyone tell the sex? I can try and take better photos if necessary.(uploading photos in a sec)
I don't have that bit of the moult unfortunately. It was difficult to remove since it was placed inside a hole in the substrate which was underneath its cork bark. I only got this one because it finally decided to remove it from its hide. I will just wait until it climbs onto the walls of the enclosure.