Speedo not working? Huh?

My friend just purchased a car and the seller emailed this to him:
Just so yo know, i took the car out for a
spin today to make sure all was well, and it looks like the accident may have
loosened the wire that connects the speedo to the transmission, so when you
hit bumps and stuff, sometimes the speedo will work and sometimes it wont. Im
pretty sure its just the wire and it just needs to be tightened.

Right before he purchased the car someone rear ended the car and that is what he is talking about in regard to the accident. My question is: Would something like that cause the speedo to malfunction? My friend wants to know how much you guys think it will cost to fix. Hell if I know how much. Thanks for any help.