I use it a lot and there have been recent improvements like keeping the searched page after selecting a card to buy. It used to refresh the page and return to the top which was a pain when you were near the bottom of the 50 card page.
I just recently discovered the seller filtering and use "Shopping Cart Sellers" when using their box option, but that still needs improvement as new searches reset to all sellers.
Searching through some sales sites tends to dissuade me from purchasing if it's clunky, but Sportlots has improved and I'm thankful for them.
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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