You're missing some important aspects of the arguments about morality.
In your example there is a series of events that happened in the shop. There will be a good deal in common among the accounts and the differences between them can be accounted for by known human behaviour and known human limitations. In short we know that there is a truth. The problem of getting at the events is due to limited evidence - in an ideal case we could do it.
In the case of morality things are different. There aren't any cases when we can show an absolute moral claim to be true. None. There are even arguments over what morality is. As I argue in the threads about morality we have to accept that in practical terms "relativism" (in the sense of non-absolutism) is true since we are never in a position to say that one perspective or another is demonstrably incorrect.
Adding to the practical problem the theoretical problem that nobody has a good model or understanding of an absolute morality (In the sense that none can even be agreed to be acceptable models of morality) and the position that morals are not absolute truths looks to be pretty solid.
In the more general case, truth can have the same practical problems associated with it (indeed if absolutism were true then the problems with morality would be examples !). However there are cases where they do not apply. Nor do we have the same theoretical problems. Either point is sufficient to invalidate the comparison.
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