I wouldn't fly Southwest Airlines if they were the last airline on the planet. Period. I hope Yelp allows me to post this review with no stars because that's what they deserve. Southwest committed THE cardinal airline sin: they abandoned a traveller who was, literally, thousands of miles from home.
Southwest has the only non-stop between Phoenix and Manchester, NH. After making my reservation and paying an extra charge on top of the airfare, I was allowed to board before other passengers. The Gate Agent entered the aircraft and sat down next to me. After about 5 seconds, she asked me to follow her off the aircraft.
I was informed that my reservation, for which I'd already paid, would NOT be honored. I was deemed a "Person of Size" and it was her decision that I needed to buy a second seat. Oh, BTW, there are no more seats on this flight (the ONLY non-stop to New Hampshire). No, you can't fly another airline because we don't "code share." Your credit card will be refunded in 2-3 weeks.
Southwest stranded me 2000 miles from my (at that time) home.
Later, after flying home on another airline, I checked Southwest's website. There was no mention of "Person(s) of Size", the need to buy a second ticket, or the Gate Attendant is the sole arbiter in this matter. Basically if you're more than 30-40 lbs over your ideal weight, you will be subject to this policy. I hope your credit card isn't maxed out.
Subsequently, whenever the topic of airlines comes up, I tell everyone within earshot of this experience. I was a business owner. I forbade my people from flying on Southwest. Yeah, they flew my bags for free; but they wouldn't let ME on the plane. How useful is that?
Now, I'm retired. When I need to return to New Hampshire from Arizona (roughly every other month) I fly US Air.