I am waiting for Josh to explain white Tahitians. They are rare so a matched pair would be even more rare. Why I think it is freshwater is the flatness of the luster. If those are Pinctada, they have a poor, flat luster, they just don't wow. The shape and the pitting are both more consistent with freshwater than Tahitian. Without knowing the seller and looking at other stuff of theirs I can't judge the reliability at all. I just don't think they look like anything but freshwaters, so I need to hear more from Josh on why he thinks they are genuine.
If they come from eBay, one needs to be very careful. You do not know what the pearls are, for sure, and want us to tell you what we think. This is what I think: Don't look for a bargain from eBay, but check out the biggest online sellers for equivalent pieces and buy from reliable venders. There are a few reliable venders on eBay but someone who doesn't know pearls is easily fooled by freshwaters. I know a lot of people who proudly wear freshwaters and claim they are Tahitians. I usually don't pop their bubble unless they ask.