I'm not sure I understand this response. If I get window/aisle, and United sells the middle seat, that's fine, one of us will move and the middle person ends up with a better seat. If that middle goes empty (and United will certainly sell it if they can; I have not heard that they are blocking middles these days), why shouldn't I be one of the lucky ones to benefit? UA already allows me to book highly desirable seats (exit rows at booking time) and in part as a result I do not buy the cheapest fares - win/win it seems to me.

As for "giving away" a seat, I don't make the decision who gets it. If its filled, it's either someone with status who books ahead, or a last minute E- seating to the lucky person who gets put into a more desirable seat than they paid for.

As for the "customer service" I am absolutely fine with any stated rules - I can use my knowledge of the rules to decide which carrier to fly. Doing it in stealth mode takes away a benefit UA has given me (advance seat booking in exit rows, and E+ seating in general) in recognition of the million + BIS revenue miles I took on them. Small bits of preferential treatment - and they are getting fewer and fewer - keep me flying on UA even though I'd save money on many trips (and it is my money these days) on other carriers.