Beware of guides who tell you that they are unesco certified and they cannot show you the badge...I made the experience that the evening before, when I booked the day tour I was shown the badge from the person who sold the tour and the next day, ( a different person)the guide said he had forgotten the badge at home.
Also he made comments (Political) which an Unesco guide would never do.
ps. the unesco guides ask for more money but they are generally very good.
nevertheless, we loved plain of Jars...very cold at this time of the year and long trip from L.P. but wonderful experience