I think the majority do value each others' collections and will attempt to work with each other. I worked out a deal with someone who didn't do a card-for-card deal regardless of era, but sought more quantity to cover the valuation difference. Most of my deals have been straightforward or with minor tweaks, while a few require major adjustments. Very few, but there have been some, don't negotiate to find common ground which is part of the fun in trading. Instead when I've fished for common ground by letting them know my desire in a counter, those few will simply decline to go further. I prefer working out a deal. Then if we cannot work out an agreement, then that's fine, too, but at least we tried.
I'd like for admin to add a feature where we identify the standard(s) we use to value cards in trade. And, allow it to be seen on the pending trade feature based on the standards agreed to.
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“Aslan didn't tell Pole what would happen. He only told her what to do. That fellow will be the death of us once he's up, I shouldn't wonder. But that doesn't let us off following the signs.” - Puddleglum in The Silver Chair by C. S. Lewis