skimilk my dear, that's a very good question.
My answer is probably not the "right" or "conventional" answer (which is: you are in the right to request more photos, and, if the seller can't provide them, you should move on).
Sadly in the reality of these things it seems as though professional sellers (especially ones that move product en masse, sounds kind of like yours that you described) have some type of supply chain fashion of merchandising their items, and, after photos are already taken, it somehow takes a light year to hear back from them for additional photos, presumably because someone has to go into some stock room and dig out the item and take photos and upload etc... which, from our standpoint, should be what the buyer is entitled to, after all, it is a very high-priced item. And I agree, 1000%. But I am only contemplating from the PRACTICAL perspective, the reality is that most large sellers will delay or refrain from doing outside of the routine factory line operations from sourcing to shipping. Principally right or not, it is the simple reality. Large volume sellers have a harder time following up with photos outside of what's already been taken.
Also, imagine if it's one of those bulk Japanese sellers like brandoff or JFA, then the seller isn't even in possession of the item, it's a mass advertising network and when the item sells the bag gets couriered to them from the shop that actually has the item in stock and they ship out to you, so, you are likely never going to get additional photos.
So, I think my slightly unconventional answer is, It really depends on how badly you want it, paired with your likelihood of finding it with a better seller who can provide more photos. And yes, it's possible you will lose out on it if you wait for additional photos. I think there is nothing wrong with asking for them and any person who blocks a customer just for asking for photos clearly isn't a business-minded entity (nor smart, either) and it sounds like this seller is (a business-minded entity). So, no worries there.
Personally, I like working with sellers who provide many photos, because outside of authenticity, there may be other attributes about the item I can see with more photos than less photos. And, I think it's just professional. And right. But those sellers I like to work with don't always have everything I want, especially if it is some dress Marilyn Monroe wore out to a dinner with JFK (I'm exaggerating, my point being, rare, hard to find). So again the question becomes is it a MM dress or is it a classic flap. Classic flap - find another seller. MM dress... well, your two options realistically are this seller or no dress. RTW... I am thinking is somewhere like 79% east of classic flap, 21% west of MM dress.
As for your rights if it comes back fake, that's the law. If you live in the United States and you purchase an item that says "Chanel" in the description and it's not authentic you have a right to your money back. It's not simply SNAD, it's counterfeit, it is contraband, it is a federal crime. (Side musing - some people are funny, I notice some friends who shop on Ebay and they won't pull the trigger if the listing doesn't say the word "authentic" in it because they feel that the seller is purposefully side stepping authenticity, but it's still illegal and SNAD since if it's not authentic then it's not Chanel/
Coach/LV etc, so the mention of the brand name as a standalone is enough without any type of "authentic" verbiage).
So, if authenticity is your only concern, and you really want the item and it's unlikely to find this from a better seller, if it were me, sure, I would just pull the trigger, assume that this reputable seller is selling authentic, get it checked out, and if it's fake, you can ask for your money back, and a return label. If this seller is a good seller, they would probably want to bend over backwards to do right by you, embarrassed that they sold a fake anyhow. If they are a devious seller, the financial transaction is on your side. It doesn't have to be Ebay or PayPal, even your credit card company will refund you if you end up with a fake. It's just a matter of headache and hassle and time.
(for the record, my main stance still is that every consumer should get their item authenticated, whether it be pre- or post-purchase is up to them, so this still applies).
For RTW, my bigger concern would be the fit... because people get things altered all the time, but that's an entirely different story...
what is TLDR?