Yes, money exchange is available right at the port, and honestly, having Vietnamese Dong (VND) is the best way to buy things in the area. Most local shops and small street food spots don't accept foreign currency or cards.

As for credit cards, they are generally only accepted at restaurants inside hotels, high-end resorts, or large shopping malls. If you're planning to eat at a local restaurant or browse the smaller markets, they definitely won't have card machines. I'd recommend exchanging some cash at the terminal first so you're not stuck!

If you were good with lower exchange rate, then sell USD at port is very easy. Bring VND with you is the best in any cases