my take: stepping out last minute (as mentioned by someone abv abt a VG) is very unprofessional imho, especially when u said u took the job and it is unlikely that they can call in any last minute backup professionals to take over u, be it videographer or photographer. ur leaving them no ground and potentially spoiling a wedding itself.
remember, u are always open to discussion with the couple. set up a few ground rules with them before the AD. let them know ur supposed to cover for them. they can have friends shooting, fine. but the bride and groom shld let them know that u are doing ur job and dun kajiao u.
while many have directly say dun take up the job, to me at least i'll say, why not? i do not sincerely believe that ppl are out to "make u get 0 shots". ppl are there for a wedding. if they get into ur way, let them know. let the couple know. there are many ways around the problem, and not just throwing in the towel. i find it very unprofessional. i'm not saying i approve of the GWC actions. but there are still amiciable ways to get stuff done. also, there is money to be earned. dun forget that.
i believe its a lot on TS's confidence itself. from his first post, i get the feeling he is lacking the confidence in his skills. being a photographer, or at least an event photographer/wedding photographer, there has to be some interaction with the ppl. by doing so, ur portraying urself not as a stranger at an event, but also someone who really has their best wishes for the bride and groom. this shld give u some leeway into some matters.
just my opinions.