[Rand Brittain]

I've been making some ebooks out of very old, crumbling, and out-of-print paperbacks, and doing my best to make them as high-quality as possible, which has led me to an ethical/best practices question. How much editing of the text is advisable when you see something that appears to be an error? I've found several old books that don't seem to have as many commas as I think they should, and while some of this is stylistic I think some of it must be in error. I've also run into sentences that can't be right like "save a thousand a year in tax each year" and had to decide what to do with them. Then there's purely aesthetic changes, like taking letters that were previously simple paragraphs and expanding them to fully-formatted letters with headings.

With the authors permanently unavailable, how much leeway should an editor allow himself? (There's probably a professional standard but as an amateur pleasing himself I can't say that I know what it is.)