Visa exemption for Russian citizens

Hello, I'm a Russian citizen and intend to visit Vietnam for 7-8 days (less then 15), which means it's not necessary for me to acquire a visa. But I'm going to enter Vietnam not through the airport, but by ferry from China (Hainan Island). I'm concerned whether I might have problems in Halong on arrival because while in the airport the personnel usually know the visa requirements well - I an afraid the sea port staff might not be that familiar with the procedures. Another thig - do I have to show the ticket from Vietnam so they that let me in? Because I'm going to travel by Open tour bus system and in a week leave from Vietnam to Cambodia, so I won't have an airplane ticket as I'm leaving by bus. Thank you for your answer=)