Reynolds experts

Hello I have Reynolds and have a question about writing a purchase order. Here is the example.
We pick up part from another local dealer, pay more for the part. Usually the 15% over. If it is customer pay what I did in the past was just input part number and not mess with the cost and then once you hit "o" to go to the "687/688" screen I would then do my plus or minus out of 687. But I was just thinking today if I am b15 on the ticket so the customer is paying what we paid cost anyway do I have to take the hit on 687. Or can I just put the part # in and change the cost to exactly what we paid for the part? Hopefully I am explaining this enough to make sense to someone out there. I just not sure if im hurting myself the way of have been doing it in the past. Please any input would be great
We pick up part from another local dealer, pay more for the part. Usually the 15% over. If it is customer pay what I did in the past was just input part number and not mess with the cost and then once you hit "o" to go to the "687/688" screen I would then do my plus or minus out of 687. But I was just thinking today if I am b15 on the ticket so the customer is paying what we paid cost anyway do I have to take the hit on 687. Or can I just put the part # in and change the cost to exactly what we paid for the part? Hopefully I am explaining this enough to make sense to someone out there. I just not sure if im hurting myself the way of have been doing it in the past. Please any input would be great