Personally, I believe that getting into caps and limits makes things too complicated--for the users, and for the coders/admins. Why not change the trade workflow to *require* new traders to send first? The higher-rated trader is instructed not to send until they receive the cards. You could enforce such logic for low trade score (<10), or if there is a large gap between two traders (one at 23 and one at 176). Let an experienced seller override that setting if willing to take a risk on a specific trade (but modify the rules and add a warning message that advises them that they may be looking for trouble and have limited recourse).
Heck, what about a warning on the trade screen if a partner has more than a certain number of open trades: "This trading partner currently has __ active trades worth $____ that are in transit and not yet completed. Many open, non-delivered trades--often adding up to large dollar amounts--may be a sign of a potential scammer. Proceed with caution and at your own risk."
Think about the amount of time and energy going into discussing an issue that is rarely a problem here (based on trade volume). Per Sebi's own disclosure, the worst case example (someone having dozens of open trades at once) is "extremely rare". And do not forget that scammers can learn any set of rules--that's why such crimes are often called "cons" (confidence games). A skilled and motivated scammer will do anything to build the required confidence to pull off the ultimate heist. Ebay had some such users in its history--sellers with stellar reputations until the day they stopped shipping and tried to disappear. What's to stop someone with one of the highest site trade ratings from simply deciding to cash in by not shipping his/her half of any number of trades? NOTHING. PERIOD. Nothing, at least, as far as the mechanics of the site go. Personal integrity, morals, and ethics are the only things that stand in the way. After all, locks on doors and windows will keep out casual or incidental intruders, but when someone with criminal intent encounters a locked door, they just reach for lock picks, a pry bar, a brick, a bump key, or some other tool to bypass your protections.
This topic comes up time and time again. It needs to be put to rest, so Sebi can focus on things that will add value to the site.
I agree with pretty much all of this. Yes, you can stop scamming by restricting the size and volume of trades, but then guess what you're making the site less-useful for all of its users, including those like me who would probably not be subject to these restrictions. Even modest trading caps could cause users to make stupid tradeoffs if not implemented carefully - eg. if a new user opens a $200 trade with me where they're sending first, and thus I'm at basically 0 risk of being scammed, will this negatively impact their ability to trade with other people because now they're $200 closer to whatever limit exists? If so, then this basically means that it becomes costlier to trade with me, and that's a problem for me.
Also, if such limits were imposed you'd see a lot more complaints about people not shipping or closing trades in a timely fashion - "I can't make new trades because of you", etc. I don't think that the perverse incentives that some of these rules would generate are being fully considered here.