Wide Area troubleshooting Boston to New York

[sp]

I am trying to prove my wide area provider is damaging packets in transit. Packets leaving Boston look good acording to my sniffer which is located on the inside of my 7206 edge router. Packets arriving in New York have bad checksum according to my sniffer located on the inside of the 2611 edge router. WAN provider is saying edge routers are responsible but I do not think so. How can I capture packets as they enter and leave the cisco routers?

[thisisshanky]

Clear the interface counters on either routers (clear interface serial 0) and then start monitoring the counters, using "show interfaces serial 0" command. If CRC errors are there, then the counters under serial interface should increase.