Dead author ethical guidelines
(My personal take on this matter - which is only based on intuition/opinion rather than experience):

When you're about to publish such a paper, ask yourself: "How certain am I that the deceased would have put their name on the paper?"


If the answer is "certain", go ahead and name them a co-author. But - explain that the attribution is posthumous, both in a footnote from the person's name (the same kind of footnote used for affiliation) and in one of the opening lines (perhaps a note as the first line.)
If the answer is "not certain", but the deceased's contribution was significant, don't make them a coauthor, but devote a few sentences to emphasize the significance of their contribution or their involvement, and clarify that the work had progressed or diverged beyond what you had worked on with the deceased (or some such explanation).
If the answer is "would probably not", and the deceased's contribution was not significant enough for co-authorship, then you just mention them in a thank-you note somewhere in the paper, same as if they were alive.




As for "preventing dishonesty" - if you're an editor or non-blind reviewer, and notice the name of a deceased person on a paper, without an explanation of the deceased's contribution within the paper - reach out and ask the corresponding author for a side-note (outside the paper) explaining the deceased's involvement with the submitted work.