I was just sold this Y. Diversipes and told that it is a female about one molt away from maturity. I find it difficult when purchasing tarantulas to get a good look at the specimen while it's in its enclosure, especially when they are being sold with their enclosure. Thoughts? Advice?
The emboli (which are a part of the palpal bulb) would be on the opposite side of the pedipalps, and are not visible here. We would be looking at the cymbium. In Y. diversipes sub-adults seem to follow the same pattern as Avicularia, and the tarsal segments of the pedipalps have the 'pink toe' setae of the leg tarsi, which this specimen seems to lack. Also, mature males seem to take on a grey colour which is consistent here.
Can you take some more photos from different angles?
It seems the seller was either very ignorant or took advantage of you. (Though it is always possible that it was just a mixup as well) i would contact the seller and inform them that it is not an immature female but a MM and see what they say.
If they won't make it right then you might look to send him off to a breeder, but most would want to know when he matured before buying or trading him.