What is there to say/suggest that truth is nothing more than an agreed common
If you wanted to say something in favor of this view, you might point to the absence of observed discrepancies between what we all believe and the truth. But, on reflection, this isn't a strong argument because there are observed discrepancies between what is commonly believed now and what was commonly believed at some earlier time. At the earlier time, p was commonly believed. Now not-p is commonly believed. If what's commonly believed were true, then both p and not-p would be true. But p and not-p cannot both be true. Therefore it is not the case that whatever is commonly believed is true.
Now you might say that what you mean is that truth is nothing more that what's commonly believed throughout the ages, the future included. So here is an argument against this revised view. There are lots of propositions about which there is no common belief shared throughout the ages: neither p nor not-p have been commonly believed. Does it follow that neither p nor not-p are true? For example, it has not been commonly believed throughout the ages that the sun is larger than the moon. Nor has it been commonly believed throughout the ages that the sun is not larger than the moon. Would you then want to conclude that neither belief is true: it is not true that the sun is larger than the moon and also not true that the sun is not larger than the moon?