Dual lifts are better than singles, scissor lifts are better than duals, and single cylinder at ther front of the trailer is best for heavy stuff. Then there is power up/gravity down or power up/power down.
Get a larger one if you can, but used if you cannot afford new. I had a 6x10 7k that ran out of space and capacity to quickly. I guess it depends what you're hauling but in landscaping it tends to be lighter bulky things like brush, clippings, edgings, mulch, topsoil, etc.... With a 7K you're looking at a payload of 4700-5000. It's good but sometimes you run out of room with the bulky stuff before payload.
I went from the 6x10 7k to a 7x14 14k. I still think it's not big enough at times. Payload yes it's fine. I also got the right truck to pull that type of a trailer but thats a whole other thread.
Get what fits your needs.
Why do you need a dump trailer?
What are you going to haul?
Do you need low profile for equipment hauling or deck over for dumping in a pile?
Can your current truck keep up with the weight of a fully loaded dump?
Just list questions and answer them. Talk to dealers and let em show you their trailers. Sit down, gather the facts, and make your decision.
Why would you be charged at the dump if you werent before?