This market is like no other because the experience here is one-of-a-kind. Not everyone would like this market for various reasons but it's still a place worth checking out!
If you know how this market is and know what to expect, your experience won't be so bad. The vendors are aggressive in that they don't shy away from approaching you, they even won't take "no" as an answer at first. Some are more aggressive than others where they will pull you. Just know that it's normal there and they don't mean any harm by it. This is where most people have the bad experiences with this market. All you have to do is say "no, thank you," and continue walking.
Vietnam is a place where there's no personal space. Ben Thanh Market is where you will see this. Vendors coming up to you, people bumping into you, and people not moving out of the way for you.
Main things to expect:
1) Vendors approaching you from all sides. They really really want your business.
2) It's hot inside there. Vietnam is a hot and humid country. The market doesn't have air conditioner.
3) You will smell things that are not pleasant such as durian, fish, and raw meat.
4) Negotiate if there's no price shown. Know your price, know the currency conversion, and stick to that price. It's ok to walk away because there will be another stall selling the same thing.
5) Negotiate hard because if they know you're a tourist they will mark it up 500% or even more.
6) You will get bumped. There are some areas where you will get up close to some people. Don't let this bother you but also make sure purse, wallets, phones, etc are kept safe. There are pickpocketers.
7) The name brand items are fake. Don't trust them if they say it's real.
My tip:
Don't buy anything right away. Most vendors sell the same things so it's good to test the water to see what the various prices are at different stalls. This market has priced items higher because it's a tourist trap. If you plan to visit central or northern Vietnam, you can probably find the same things there but at a lower cost. For example, the fake Adidas shirt I bought at Ben Thanh was for $4.40. When I went to Hoi An, Vietnam, they were selling it for $3.50.
Make sure that if you are talking to them, that you have a clear path out of the stall. They will use tactics to make it hard for you to leave because they block you in hoping that you will breakdown and buy it.
Be nice to the vendors even if they are a little pushy and charges you more because you're a tourist. I don't take it personally, I see it as the culture and just go with it.
Try the food court - don't be scared.