If you’re from one of the 93 countries allowed to enter visa exempt - that is with no visa, just a free entry stamp - then you’d get 60 days on entry.
There is no free visa for 30 days.
Bear in mind that the day you enter is day 1, so you will be stamped in for 59 further days.
Do the math and work out if you need an extension and if you don’t get one that you’d be happy with an overstay stamp and possible fine for the one day over.
There has been a couple of posts of people being questioned about why they got their DTV in xyz country and not their home country but I don’t believe there has been any mention of actual denials.
You can’t renew a tourist visa. With one you’d get 60 days on entry.
Most nationalities can extend that once for 30 days.
I suspect you may be referring to border bounces where you briefly leave Thailand and return for a fresh entry stamp.
If so the answer is that there is no official limit. It’s up to the immigration officer to decide if they will let you in.
They are getting tougher on these so if your relative wants to do this then probably best to use an experienced border bounce company as they generally ensure you can get back in.