If you conduct infrequent transactions which are also small, you’ll never lose much money and it’s not worth it to try to protect yourself – you’ll sometimes get scammed, but you’ll have no trouble affording the losses.
If you conduct large transactions, regardless of frequency, each transaction is big enough that it makes sense to insure the transactions or pay an escrow agent. You’ll have occasional experiences of fraud, but you’ll be reimbursed by the insurer or the transactions will be reversed by the escrow agent and you don’t lose anything.
If you conduct small or medium-sized transactions frequently, you can amortize fraud losses using the gains from your other transactions. This is how casinos work; they sometimes lose a hand, but they make it up in the volume.
But if you conduct medium-sized transactions rarely, you’re in trouble. The transactions are big enough so that you care about losses, you don’t have enough transaction volume to amortize those losses, and the cost of insurance or escrow is high enough compared to the value of your transactions that it doesn’t make economic sense to protect yourself.