Super late to this party, but I'm bored this morning and came across this post.
It's something I've had on my (admittedly lengthy) profile for a while.
I will give up extra value to entice someone reluctant to part with a card. I'll give up extra value if I'm trading up into your reserve list card or something.
But if you say flat out "I don't do any trades where I don't get a 15% premium", you can fuck right off.
They often cite store buylists when I challenge them on that attitude of entitlement. Sure, stores buy low and sell at retail....but think about what a store provides. They give you confidence of dealing with an actual business that can be held accountable for any number of things. They provide a nexus for the community by providing a space for gaming, running events, marketing said events to attract players, etc. You support your local store for the convenience of not having to wait for things to come in the mail, but also because of the intangible value you're purchasing that you might not necessarily notice.
The guy on here claiming to be "a store" and demands a premium? Even if you own a brick and mortar store and this is a sideline (doubtful), so what? Your "store" is 1500 miles away and provides nothing to me beyond the awe-inspiring privilege of trading a card with you.
I'll be honest, I've been working on and off on my own trading site to fix a lot of the flaws I see with systems like Deckbox and PucaTrade. The biggest is lack of feedback options.
My partner is getting her PhD in Behavior Analysis, and one of the FIRST things talked about in the OBM unit of the intro class she teaches is that binary feedback scores are utterly useless. Trade feedback should ideally use a Likert scale, something you're probably very familiar with from any satisfaction survey you've ever taken from a restaurant or whatever: 1 (strongly disagree) -> 4 (neither agree or disagree) -> 7 (strongly agree). Further, there should be more than one metric....overall satisfaction with the trade, trader was easy to deal with, shipping was fast and things packed appropriately, etc.
Especially when deckbox almost never allows negative feedback to be used, a binary positive/neutral/negative is useless. A graded scale and aggregate averages also smooths out anomalies. My own profile has a neutral here and there that were simply retaliatory dings when I had a legitimate complaint about my trade partner and gave justifiable neutral feedback. That only really gets smoothed out when you have a few hundred trades like I do....for most, with under 100 trades, a numerical score is much more helpful.
Lastly, I'd add feedback for attempted deals. How quickly would people be motivated to keep their tradelists in order if constantly turning people down saying "that card isn't actually for trade" resulted in a trend in their feedback that warned others away from dealing with them? This would go hand in hand with the original problem in this post, people demanding trade premiums. Suddenly, there's a feedback trend showing the reason the deal was declined, and you can see most of his trades don't connect because of pricing differences? You know to avoid that guy, he gets fewer trades, and consequences shape a change in behavior.
That's my rant on the matter. It's a problem I see not only on this site but all over, with people sitting down IRL with me at GPs, spending 20 minutes going through each other's binders, only when it comes time to close the deal they suddenly add "well, I only trade if it's in my favor, let me add a few more 'small' things to balance it". It wastes everyone's time. Everyone thinks they're clever playing with cardboard stocks, but really they're just hurting this game and community to squeeze out a negligible profit.
Most of the time, their speculating and flipping cards nets them very little, or often they even lost money, and then they give up; I have a number of people at my LGS who tried it and failed miserably after months of self-delusion that they were making so many imaginary dollars.
My advice in the meantime: Do what I do, make it unambiguously clear that you don't tolerate those people. If no one traded with them, they would go away. It would happen quicker if we had a useful feedback system, but with how primitive this site is, the best we can do is ignore them individually for now.