How is a buyer supposed to trust that the scalper won't just run away with the money? And conversely, how is the scalper supposed to trust that buyers aren't just feigning interest and will back out at the last minute?

Even escrow systems don't necessarily bypass this because ultimately the buyer is likely spending on more than just the concert ticket. They're probably taking time off work, maybe traveling in from another city or country. So even if they might get their ticket money back if the seller backs out, by the time that happens, it's too late to get refunds on everything else.

And combined with the possibility of getting lower prices closer to the event (extra drops from the event, honest resellers who just can't make it, scalpers trying to cut their losses), even buyers wouldn't commit early to scalper prices.

Maybe limit total number of transfers among all tickets. Because it should be a small minority of legit transfers.

Scalpers should be less likely to take a chance their transfer will be denied, whereas to a legit customer and friend ticket is otherwise worthless and just a best effort anyway.

Or beyond the first X% of transfers you do more rigorous validation. Like asking for the original buyer to call in to confirm in realtime. Something not easily automated.