agree... it is only 1 day, but most would agree it best to pay 1,900thb at immigration for an extension rather than risk getting caught within that '1' day overstay for whatever reason (traffic stop/accident/dispute on final payment etc) and get deported and banned.. also not good idea to have any 'red' stamps in your passport.
if he goes to immigration on day 89 and acts dumb and wants another ‘30’ days (attempting to get 7 more days, do you think Immigration will give him ‘7’ days extra to ‘get out of Thai’?