OP, you’ve gotten plenty of responses regarding graded PSA cards, so I’ll give you my perspective on raw card buying/selling etiquette since that’s what I am most familiar with.
The price of the card and the amount of cards determine the effort both the buyer and seller should put in. Effort trends upward with increasing effort and downward with increasing quantity. The more expensive a card, the more effort required. The more cards, the less effort required. The greatest effort is required for the most expensive and least amount of cards. The least effort is required for the least expensive and greatest quantity of cards. This goes for both buying and selling.
Here’s an example. If I’m selling a complete set of, say, Fusion Strike, I’m not going to take pictures of all 284 cards and 217 reverse holos - it simply wouldn’t be worth my time or the buyer’s time to look through every card. Likewise, if I’m the buyer, I’m not going to ask for pictures of all the cards either. That goes for every set, even vintage. If a set is listed as NM, I’m not going to ask for detailed pictures of every card. If I really want extra pictures on a listing for a complete set, I’d ask for pictures of the most expensive cards, the cards I personally care about most or the cards hardest to find in NM condition (usually these go hand in hand). Maybe I’d ask for back pictures page by page if I was truly concerned. My philosophy is, the more I am spending, the more certain I should be that what I’m buying is as advertised.
If I get the set in the mail and a few cards are less than NM, I won’t ask for a refund or return. However, if I asked for specific pictures and damage still isn’t shown, I will ask for a return. I don’t like refunds because then I’m left with a card I don’t want. I’ve bought thousands and thousands of cards online, and I’ve only ever needed to return one. Additionally, if a majority of cards from a NM listing are LP, then I think it’s fair game to contact the seller. All that you both lost is time. You can usually avoid this by training your eye to catch signs of damage in pictures. Is the binder, sleeve, or environment dusty? Is the card sitting raw on a random surface like a table or bed? Is the lighting dull or not reflective off the card’s surface? I almost instinctively avoid those types of listings altogether.
It’s important to note, however, that NM is NOT synonymous with “pack fresh”. NM does allow for imperfections. Surface scratching is probably the best-hidden damage in cards and is what I encounter the most when buying, especially on eBay. However, low amounts of surface scratching is still technically near mint. Buy NM expecting NM and hoping for pack fresh, but if you really want a pack fresh vintage card, you might as well buy it graded 10.
Here’s my take on buying from sites like TCGPlayer and TrollandToad. Never buy anything high value without pictures, and keep in mind the relationship between effort, price and quantity. I buy hundreds of cards at a time from vendors on TCGPlayer without pictures. I only reach out to the seller if the amount of cards less than NM is a substantial portion of either the quantity of cards, or the amount of the order. For example, if I order 100 cards in NM and 10 arrive LP, I’m not going to complain. If 25 are LP, I might contact the seller. If 50 are LP, I’m definitely contacting the seller. Alternatively if my order is $13, and one $10 card is damaged, I’m going to contact the seller. But if a $1 card in a $13 order is damaged, I’m not going to say anything.
Ultimately, you have to judge what is and isn’t worth your time and the seller’s time to fix. If you can prevent a situation as a seller, do it. If you can avoid a situation as a buyer, do it. But sometimes there is no preventing or avoiding. Sometimes, when you order almost an entire set of SM Ultra Prism from vendors on TCGPlayer, half the cards arrive played or damaged simply because they were stored improperly at the TCGPlayer Warehouse. So you have to reach out and ask things to be set right.
ALWAYS be polite and NEVER accusatory! Most people want to sell without a hitch and not have to deal with people or problems directly. However, the reality of selling online means you open yourself up to that risk. Only push for a refund or return if the money is truly that important - in which case, you should probably also look at your own life choices to determine why you spent that valuable money on cardboard. Then change your choices so you don’t spend money much needed on cardboard in the future…but I digress. Ebay has their “product not as described” button to protect buyers against malicious and even ignorant sellers. Use it, but don’t abuse it. Same thing with TCGPlayer and most online marketplaces.
My thoughts were kind of all over the place here, but hopefully this helps you somewhat, OP.