Different species have different 'tell tale' signs for females. Some have a prominent 'lip' at the furrow, while some others might have a very obvious 'moustache' of contrasting hairs. It matters, or else people wouldn't ask for it.
And size is not really required here, since there is a hand in the photo that you can ballpark to, although people should really get into the habit of providing both.
@VanessaS@Mvtt70 Well I had thought it was A. avicularia. Yet all of them basically look the same, except for this one. This sling is bigger than the others and it's color does not resemble the 7 other A. avicularias i own. It might be a C. laeta, but I'm not 100% sure. Yes i know...shame on me.
@FrmDaLeftCoast Those legs are far too light coloured to be an Avicularia avicularia. I would take a dorsal photo and put it in for identification, but if the only two options are Avicularia avicularia or Caribena laeta, then I would go with C.laeta.
I would also go with them being female.