Vietnamsvisa.com seems to be legitimate.....
Plenty of scams for getting a Vietnam Visa.....
There is a list from the Vietnam Government website.....
"We have the honour to announce that the following websites are not legitimate":
, Vietnam Visa on arrival | Apply Visa Online - My Vietnam Visa
, Vietnam Visa On Arrival - Visa Vietnam Online | Vietnam Visa Corp
, Vietnam Visa On Arrival | Apply visa online for business & tourists
, Vietnam visa | Official site of Vietnam Visa GOVT ?
, Kloxo Control Panel
"There has been an increase in the number of Australians applying online for a ‘visa on arrival’ approval letter. There have been reports of visa scams involving online Vietnamese visa applications. There have also been reports of applicants’ personal details being made public by online visa websites. As result, we recommend you apply for a Vietnamese visa directly from the nearest Embassy or Consulate of Vietnam."
See the official Vietnam Embassy site - easy to apply:
The Vietnamese Embassy in Australia - Consular