We applied for our Visas from Canada. If something is incorrect with the info submitted they will ask for it to be corrected. They won't just reject you. The Embassy in Vancouver is very helpful too.
We dealt with Yorick Karl from AA Insurance brokers and ended up choosing Pacific Cross. He was extremely helpful and answered all my questions...and believe me, I had lots! We haven't had any claims yet so I can't comment on that issue.
We were ready to do everything ourselves but ran into problems when we went to open a bank account. The bank said they changed their policy and had to have a longer visa, 90 days didn't meet their rules. After that we didn't want the headache and decided to use an agent. We couldn't open just a bank account, they wanted to do the whole thing. We used Siam Legal in Phuket. They were very good and it provided some peace of mind.