Those really large Tahitians are probably from the third seeding, and I've learned from previous discussions here, they don't have the great lustre the first harvest pearls do. Like the ringed pearls, too!
I don't know this dealer--but 15-17mm tahitian are extremely rare. You're right about 3rd seedings having lower luster, but if you find a strand that is that big and does have excellent luster, $30k probably isn't an unreasonable price at all. However, if I were going to spend $30k on a strand, I want to see the strand in person or--if that's not possible because of schedule or location--I would hire a qualified a appraiser from the vendor's area that can examine them and give me an independent assessment before purchase. Better to spend $500 on an examiner, than to buy a problem.
I have had communications with Pearl Society in the past and found them to be responsive and they have a good reputation. In then end, I haven't purchased from them because, even though they have an ok return policy. Dealing with shipping issues to and from HK is never fun--and if there is a problem for any reason, you have no meaningful recourse (aside from a bad review on ebay). I have also always been able to find US ecommerce retailers that offer similar products, at similar prices, without the hassels.
Right now, the major PG contributors, Pearlparadise.com, pearlsofjoy.com, don't have anything in this range. American Pearl has three baroque strands for $450, less the usual 10% coupon. I am not in love with their 3 $450 strands, but this one is ok: http://www.americanpearl.com/aphol1027.html
I have been there and will probably be moving again in a couple of years. Pearls can wait--for a little while anyway. But a nice freshwater strand might hold you over for a while if you need a fix for the addiction. :-)
We bought our first place last year, and it needed new walls, floors, kitchen, bathroom, etc. And now we've moved in, we need bookcases and curtains for our MASSIVE windows (the living room window is 148 inches wide, and the bedroom windows are 130 inches wide, and that's an expensive lot of material).
So, sadly, pearls have to take their place in the financial queue, even Tahitian pearls.
this sort of problem is so common on ebay. to make matters worse. the people that buy don't know any better and then when they come across a real tahitian pearl pendant at a realistic price for a genuine tahitian pearl they think they are getting ripped off, when initially they were the ones ripped off.