You know, as a business, you can accept zero confirmation transactions from both BTC and BCash.
For BTC = just wait 10 seconds. Even a cup of coffee can wait 10 seconds. It's zero confirmation, but you can almost safely accept the transaction if there are no double spend attempts after 10 seconds.
For BCash = just wait about 10 seconds also. Maybe 20 if you want to make sure. After a confirmation, send it to an exchange and market sell.
For anything else that costs more than a cup of coffee, I'm sure you can wait 10 minutes for a block; and if the transaction hasn't confirmed yet, it should in a few.
For BTC = just wait 10 seconds. Even a cup of coffee can wait 10 seconds. It's zero confirmation, but you can almost safely accept the transaction if there are no double spend attempts after 10 seconds.
For BCash = just wait about 10 seconds also. Maybe 20 if you want to make sure. After a confirmation, send it to an exchange and market sell.
For anything else that costs more than a cup of coffee, I'm sure you can wait 10 minutes for a block; and if the transaction hasn't confirmed yet, it should in a few.
Not any longer. BTC broke that model with the introduction of RBF.