When a customer purchases or does anything with bitcoins, he/she would have a track of it. All transactions can be monitored at any point. It helps save more money as well. No third party's involvement. If more bitcoins are used, then many merchants would start accepting it. Its very comfortable for them as they no need to go to bank for any other transaction they make. There are many other good reasons why customers use bitcoins.
you can track your payments, but to a certain extend it's quite pointless as merchants use payment services for their bitcoin payments, and thus not get involved in the transactions at all. they just get a notification that the payment went through with as result that you get the goods you paid for. so yes, in this case there is indeed a third party involved. merchants do that so they are not exposed to the risk that the volatility brings with it.