I've done a lot of transactions (40+) on here, both buying and trading in both strings and racquets, so I thought I would share some of my experience as it pertains to string trades.
String Trades: Personally, I've never had a string trade go bad. If you're going to trade strings with someone, make sure you feel like you trust the other person (check references beforehand) and make sure you feel like you're getting a fair deal both in quantity and quality of string. Nobody like to feel like they're getting treated unfairly or that they're treating someone else unfairly.
If possible, go buy some small zip-ties and put at least 2 of them around each set or half-set of string that gets cut from a reel to keep the string from kinking or getting tangled up. You can find them at hardware stores and they only cost about $5 for a pack of 100 of them.
To keep the string exchange shipping costs down, find a padded (bubble mailer) envelope to use and ship it via first class mail. The total cost should only be around $3-4 (1.50 envelope + $1.50-2.50 to mail). Make sure there aren't any sharp tips of string too loose that could poke through the envelope. Also make sure to securely tape the end of the envelope if you're worried about the existing adhesive being strong enough.
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