London embassy. No stamps needed to be shown. I made sure all the documents I sent were enough so no questions were asked. I was worried they would call me in for an in-person interview or ask for proof of flights but it got approved pretty quickly without any of that.
Ask the owners of this group to help. I got mine without leaving Thailand (e-visa). I just need to leave and come back to get the first 180 days stamp which I am doing this weekend. But I have already been approved for DTV with documentation.
If you use a good agency you can apply online (evisa) while in Thailand. That's what I did and got it approved in around 5 days once I collated all the required documents. I just need to leave and come back to start it which I am doing in 2 weeks. Visa 10k baht. Agency fee 20k. Still crazy-cheap even with the fee.