@Mea***
&
@Ma***
let's get some terminology out of the way so you two know what you're talking about.
There is NO such thing as a 30 day visa on arrival :O A visa on arrival is for 15 days, it can't be extended for 30 days and it is available to people from 18 countries only.
IF you didn't buy a visa from a thai consulate before you came here and were stamped in for 30 days for free you got in on a 30 day visa exempt entry.
Be that as it may. No one is gonna be able to tell you IF you're going to get pulled aside stamping in on a new 30 day visa exempt entry when flying in. It's down to the mood of the immigration officer you're standing in front of when you stamp in.
All you can do is be prepared with the 3-proof-ofz
proof of 20K baht or the equivalent in CASH
proof of onward travel (within 30 - 60 days)
proof of a hotel booking or confirmed lodging.