I was under the impression that no matter how many players you have, you should play with (up to) 2 core sets, and one of everything else, and that if you buy multiple copies of the expansion packs, you are (very mildly) cheating by make for easier deck building possibilities.

I became less sure when I saw people talking about playing a 4 player game with *six* copies of Delve Too Deep. I'm playing 4 player and we have exactly one copy of The Miskatonic Museum, which is what I thought you were supposed to do, which gives us 2 copies of that card.

How do people feel about buying more copies of an expansion pack to get access to more copies of a card, in a 4 player game?

Players are supposed to bring their own cards so each player can use a pack themselves.

There is no collective limit for investigator deckbuilding (except that all investigators must be different, due to the uniqueness rule). It's only for basic weaknesses and scenarios that you have to use only 1 copy of each product (including the Core Set).

Every player's deck is limited to 2 copies of a given card (unless otherwise noted). (Weaknesses & scenario cards are limited differently.)

We tend to run many copies of Charisma (which lets you field an additional ally). For permanents, we proxy. Everything else we run physical copies and are limited to 2 (except core cards) because we only use my collection. There are a few cards we would use more of (Lone Wolf comes to mind) but so long as you don't break the deckbuilding rules you can run as many of a given card as you like. We build our decks in different directions and different classes, so past level 0 it's really rare that we would even want take the same cards.

It's not cheating at all in any way. They already have limitations built into gameplay and deck construction. You're more than free to buy multiple copies to beef up selection for multiple players. There are cases where people get together and each person may have their own collection - you're not obligated to build all player decks from only one collection.

The main rule of thumb is two copies of any one card title per player deck, with the exception of exceptionally which allows for only one copy per player deck. The idea is that players have their own collections, and collaborate as they deck build. That said, it isn't always the case. Often times, one player provides the collection, and players build from one collection. It's done with my friends and my collection. It was done at the last Invocation I attended. (I made my own deck, but everyone else used the collection from the host). There is nothing that says one player cannot have 3+ cores and 2+ everything else, just as long as you follow the deck building rules including rules for exceptionals and exiles.

I know people who have 4 cores and 2 of everything else (except standalone scenarios), to be able to provide for a group of 4.

There is no limit on cards at the table, the only rule is that only a single copy of a given Unique card can be in play at a time.

Unique cards have star symbols in the name.

This is the rule that prevents you from having 2 Rolands at a table or 3 Peter Sylvestre's.

I used second hand sellers to get me extra copies of common cards like Shortcut and Rite of Seeking.

Thanks everybody!