Does any one know the if the 7 day extension for after your 60 days for 1300 is actually a thing and if so is it a "bad stamp to have in your passport

Hello everyone at the Visa community! I need some advice about the 60 day-visa to Thailand, Hua Hin! I've signed a contract for a long-term house. I was told by a visa agent in Bangkok that I could extend this another 30 days. Now she advised me that she needs to have now a flight ticket with me flying to one of the border countries, otherwise the Thai embassy will refuse my 60-day visa! I was under the impression that I could do a border run to Cambodia when I arrived at Hua Hin! So I need the communities advice on this urgent matter as I will arrive in Bangkok on Sunday the 30th of April. I'm using the agency BaanSmile and they said they could help me out with the 60 day-visa! I'm an Ex brit squaddie who has been living in Germany for many years now.

Applying for 60day visa from UK. They asked for this doc what is it ?