it took two weeks for them just to tell I applied to the wrong location, but they still took my additional information so I thought they were going to process it. Finally after two months nothing happened and they definitely told me I had to use los Angeles which is my location. I just reapplied 4 days ago, so I'm waiting.
I applied to the wrong location New York out of being to anxious, so yes guidance is recommended unless you know you have all your documents and procedures while applying.
I'm hearing that agents are charging enormous fees despite there's only one portal you can apply on which is the Thai e visa website. I would recommend only getting support and direction, but apply yourself. Support is highly recommended in my opinion.