You only need to collect what is described in the text and photo in the ad. Should the advertiser ask for more, it is up to you if you want to take that too. Otherwise, you can ask the advertiser to post another ad and select you for that one too, or take someone else if you are not able to take it.
In the worst-case scenario, you can cancel the collection and describe the reason. Remember that cancellations drag down your statistics for completed ads.