When describing objects in telling a story, should the objects be referred to in past tense or present tense, if the effects of the story still hold true on them? Since it is a story it should be in past tense but if the objects remain the same to the present time from the story it should be present tense. Correct me if I'm wrong, but isn't it poor grammar to mix past and present tense in a sentence?
I thought of this when writing the following: I just bought something from the deli at the grocery store and was surprised my receipt had one number.
Should it be had or has? I still have the receipt and it still has one number. A simpler example is "The man walked into a room that had red walls." vs "The man walked into a room with red walls". Assuming the walls are still red upon the telling of this story, which is correct?
Furthermore, I notice when people are unsure if something is untrue they tend to use the past tense. For example if there had been a car crash and someone observed the backed up traffic but left the scene before they saw the traffic resume to normal flow, they would say There was a car crash and traffic was backed up. I'm not sure if it is flowing again. Is common to speak of things in the past tense when unsure, for example why not replace was with is or is either acceptable?