I agree.
If you want it and phone up for it, go and collect it.
If you are not going to go just phone up or text, even if its a quick "sorry not coming call", just politeness isnt it?
What Paul says (NYRS) is a good comment, sold it earlier as didnt know if you were coming. You would be miffed so works both ways. Lets hope trust remains within the RSOC as it always has