ok I am going to comment based on what I am reading as I read it so if it get jumbled, I apologize.
First, I don't like the dollar limit on any tier. I think perhaps a limit on the active number of trades is a good idea. if a new trader has a goyf and wants my cards, I don't think it is fair to prevent that. the tracking and sending first helps prevent scammers at first.
second, I like the idea of enforcing the person with fewer confirmed trades to send first. However, if an experienced user is not doing this already, shame on them. I have only had one problem with a new user and I feel bad for him, however he chose not to use tracking and did improper packaging so it's not my problem. I do disagree with making it a lower sends first in all cases. I am close to 400 trades now and why would I want someone with 300 trades at 100% positive feedback to send first. doesn't make sense. I think there should be a cap at tier 1 as 20 trades and tier 2 as 50 trades.
third, having a credit card on file is not an option for me. I use paypal expressly for that reason. there have been way too many security breaches to start giving out my credit card number to every site I use.
forth @Zyron, I personally have 2 accounts. I manage them for different purposes and also (before premium) traded to myself to move cards from one account to the other. I also have noted on my profiles that the other account exists. If someone was to try to do some shady things by "trading" between accounts they created, that is of course a bad thing. I personally check the references for anyone under 30 confirmed trades to see who they have been trading with to ensure nothing shady is going on. I also check the "member since" to see if the shady things mentioned above could be happening.
fifth, if anyone is doing a thousand dollar+ trade and are not using a third party for the exchange or meeting in a populated place, then sucks to be you. this only makes good trading sense. many local gaming stores are happy to do the exchange. I see comment about a mediator. I for one think that is a great idea. this site could leverage willing traders with high trades counts as mediators for high value trades. there would be extra expense (to the senders buy sending postage value to the mediator's paypal) and time delays but as long as the mediator is verified through their address and paypal, this is a great alternative.
sixth @Amurpcs, stopping new users from selling is not a good business idea. the fact that sebi enforces people to use paypal, adds the security that is needed for buyers. they can do a chargeback through ebay if needed.
seventh @AuspSqueeky, always leave accurate feedback even if it is negative/neutral. if your trading partner does leave retaliatory feedback, open a ticket and sebi will reverse it. I have had experience with this. dude was pissed because I wouldn't take a different edition of the card worth 25% less than what he promised. left me negative feedback saying "trader is too picky". sebi reversed it to neutral feedback which is appropriate. Although sebi, I have asked in the past and would like to state it again. keeping feedback hidden until both parties have left it, is a wonderful idea!
eighth, I like TechnicolorMage's idea on expanding the feedback option. I have to say that at least 1/3 of my trades have come in with a problem (ie wrong set, bad condition, missing card, etc). most traders are very quickly fix the problem but sometimes it isn't worth the hassle for a 10c card. for those of us who have collections of playsets this would be a great way to give a lower score for the issue but still leave positive feedback.
ninth @sidewayzracer/Amurphcs, buyer feedback is a decent idea. ebay does it and it shows that you are active on the site like Amurphcs states and not some inactive scammer. perhaps not even feedback but just a tally of how many purchases you have made through the site.
tenth, I talked about it above but I cant find it now. I think that limiting new users to current trades in route is a better idea than a dollar cap. I think that 3 is too low though and that 10 would be my max until they hit the next tier.
tenth @sebi, I think this site is amazing and I consistently tell everyone at my LGS how awesome it is! thank you for an RFC on such a big issue as this.