A little while back the wife and I were looking at heading west and Southwest had the lowest fare last minute by a fair margin. If we were going economy class, the wife and I wanted a little extra room to spread out, so we purchased an extra sea (even with that extra seat it was less than DELTA or AA were asking for two seats in economy). In fact we could not figure out how to book the extra seat on-line, but a simple call to Reservations and the agent was able to process our request without issue, she did not say it was impossible or not allowed (though I can clearly see from the above quoted rules that it is).

At the airport the agent had zero issue with us and said she wonders why more customers don't book an extra seat and since we had like A20-21-22 it worked out that we had an entire row to ourselves, ironically after the flight we did get a refund for third seat (which we never expected nor wanted) and I tried three times to get Southwest to suck back the money, but they claimed that they did not have the ability to do so, in fact the last Agent that I spoke with said that most customers call in demanding refunds and that she appreciated my honesty and that I should not worry about it.

I now realize that from reading this thread that Southwest refunds customers who require a COS seat but that due to the flight not being full are not required to pay for it, I guess we benefited from that even though neither my wife nor I am/are COS.

We have booked extra seats in Economy on other airlines (and it does not seem to be explicitly not allowed like Southwest clearly spells out) when we fly Southwest from now on we will NOT do so as we do not want to run afoul of their rules as we genuinely like Southwest.