I did all of 2016 on visa exemptions, extending each one to 60 days, 2-3 weeks out between each trip, I took pics of my stamps and posted on Thaivisa forum, Google jspill 9 back to back visa exemptions if you wanna see (new here but been over there years). Even with a 2 year overstay stamp in my passport and in total 7 years in Thailand.
Maybe I just got lucky as I know some friends who got denied entry after 1 year stay and had to buy a flight ticket home there and then in the airport.
If you search bkk airport fast track immigration there's a service where for $30 you can use the fast lane at passport control, same one Thai Elite card holders use, and a rep meets you as you get off the plane and takes you through 'to assist with the speed of passing immigration'.
One mate who got deported used that and it worked, he got back into Thailand. It makes you look more 'wealthy' or whatever. I'll use that next time I fly in, at the moment I'm 'cooling off' in Philippines a couple months, I think as long as you take trips outside Thailand to a range of destinations you have no worries with visas. It's only an issue if you try to spend as close to 365 days a year in Thailand as you can, always go to Cambodia for 1 night then fly back, etc.
Also always have 20k baht in cash on you when passing through airports, sounds ridiculous but that's the criteria they use for 'proof of funds' to support your stay. A rented onward flight ticket from flyonward or bestonwardflights can help too (latter is faster and cheaper, $8).
Airports are pretty risky lately though if you have a long visa history so another hack is to fly to Laos and come in via land border, there's a private car lane which based on reports just waves you through, rent a cab from Vientiane to Udon, have your tourist visa from there (easiest consulate to get one) quickly checked as you drive through. Even if denied entry at a land border they often don't put the denied entry stamp in your passport, so you can simply try again, try a different border, or fly in as a last resort. Can't do more than 2 land border entries a year though, recent change.
Here is one friend's denied entry stamp (personal info cropped out)
In thai it says 'career, and lack of funds' these are always the reasons - to avoid the latter you show 20k baht in cash (sometimes other currencies that can be converted to baht are accepted, or travellers cheques, but to be safe have baht). For the former you need a good story as to how you are not illegally working in thailand (as a bartender, tour guide etc.).
Can help to have a Thai girlfriend or landlord on speeddial to call and back up your story too in the event you get pulled aside and questioned, which is happening more and more lately.