Thanks for your reply.
Indeed, what you pasted in above seems to make some sense. For now I changed the old url from /merchant1/info/terms-of-sale to /merchant1/terms-of-sale and it works.
It seems too many forward slashes /'s cause it to fail.
I've looked online but couldn't find clues regarding the additional syntax I need to setup mod_rewrite. I've also encountered references to RedirectMatch though this is more suitable for redirecting groups of url's in one go.
If I can find the extra code I'll make the old url's longer, if not I'll keep them short (only one /).