I don't think any of those "rules" should be "mandatory". I think it depends on the amount of cards and value of the cards. I often put two cards in a penny sleeve, especially if the cards are low value to begin with. Not only is it economical but it makes them tighter and less likely to slip out. Usually cards valued at $5 or more, I'll penny sleeve and put in a top loader. I also usually use team bags.
My biggest pet peeve, other than receiving unexpected damaged cards, is tape on a top loader. I don't know how many cards I've received that are ruined because they slipped up out of the top loader and got stuck to the tape used to seal the top loader. Put a tiny piece of paper (post-its work great) over the top loader and then tape over the paper.
Bubble wrap packages should probably be mandatory unless a PWE has been previously agreed upon.
My biggest pet peeve, other than receiving unexpected damaged cards, is tape on a top loader. I don't know how many cards I've received that are ruined because they slipped up out of the top loader and got stuck to the tape used to seal the top loader. Put a tiny piece of paper (post-its work great) over the top loader and then tape over the paper.
Bubble wrap packages should probably be mandatory unless a PWE has been previously agreed upon.
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