There's usually different ways of looking at it. In my F/S threads, I always post that "I'll take it" time stamp rule applies for email, PM, or post. Some others do while some don't.
That aside, I think most people want people to post "PM sent" or "email sent" in F/S & F/T threads. Whether we like it or not & even if those posts don't "do much", they do bump a thread. & of course, you'll usually see a post by the OP stating that they replied to the email or PM. It's all about bumping the thread whether we like it or not.
I'm not complaining, just explaining. The best thing to do is post "I'll take it" & see what happens. If you missed out, you missed out. If the OP stated that the first "I'll take it" gets it, then the person who posted that they sent an email or PM doesn't/shouldn't get it. Simple.
Like the Mods said, I don't anyone wants too many strict rules. However, I also understand where the OP's coming from & his frustration. I'm not sure there's a method that will please everyone, unfortunately.