It may not be a problem getting a room, as said it may be quite easy.
Personally, I would book anyway as I little or nothing to be gained by doing it.
You will arrive in Patong with you bags, perhaps you'll pack light, but with bags nonetheless.
What are you going to do?
Walk from hotel to hotel to the better room and/or the better rate?
How many will you visit before making up your mind and how detailed will you be?
All that - while treading a long with your bags in 100ºF/35ºC and high humidity, maybe even rain. Besides the discomfort that I can envision during the mission to find the little bit better deal, I personally would hate to spend my pressures time on that, especially if was only for a weekend.
Of cause you could let the taxi driver recommend a place
If you and I were to arrive on the same flight you would likely be just checking in all hot and sweaty at the time when I am paying for my first Thai massage.