I wasn't aware that new people MUST send first. Come to think of it, that's definitely a good way to discourage people from running off with your stuff. I imagine that the recipient will be the member that's more known in the community, someone that has developed a bit of a reputation for themselves?
Here's what the first rule says:
a) New members with less than 10 Feedback MUST SEND FIRST on all Trades/Sales.
So I misspoke a bit. New people USUALLY have to send first. I'm guessing if there are two people who have no previous trades completed, it's up to those two to decide, unless this applies:
Be alert and check your trading partner's profile for a "Must Send First" tag. This tag is placed on a member's profile for a reason!
The rest of the guidelines for selling/trading can be found here:
http://www.sportscardclub.com/threads/trading-selling-guidelines-updated-7-30-13.427258/
As for shipping, how much does it typically cost to mail a card or two? I assume there's a hard sleeve or case involved to prevent damage?
The following is in my opinion (IMO):
Cards need to be protected during shipping. They need stiff backing to keep from being bent or dimpled in transit. An ordinary envelope isn't advised, as damage can happen relatively easily in them.
A bubble-mailer works well for small numbers of cards, but cards should be placed between something stiff and hard to flex, like stiff cardboard or thick plastic. It costs about $3 with USPS Tracking (recommended). With a medium-sized bubble-mailer you may be able to fit up to ten cards or so in it safely, and that may be an extra buck, maybe $4 total, but I can't say for sure as I never used the larger kind, I use size # 000 lol
Larger amounts of cards should be sent in a box. The box should be at least two inches larger in dimensions than the cards. The cards should be wrapped carefully in something to contain them, like a hard-plastic box (the kind made specifically for trading cards) or plastic or paper wrapping. The goal is to keep the corners from being damaged while being wrapped, so hard pieces of material (like cardboard) should be "sandwiching" the cards before wrapping them and taping it closed. Once properly pre-packed, the cards can be placed in the box with packing material, foam peanuts, newspaper, etc. spread evenly around the cards, at least an inch on all sides. That'll protect the cards from most damage...unless one of the handlers throws a mean fastball with it, then I make no guarantees.