It's one thing to buy a cheap Chinese impact that in the worst case is a non-functioning POS- or wears out in a year. It's another to buy something that you'll be lifting objects and standing underneath them.
We had one of the Harbor Freight floor jacks in the shop. It came in somehow and it was one of those "it won't get used much..." things so what could it hurt. It was rated at 5000 lbs. It collapsed with about 2/3rds of that weight on it. Literally bent like a pretzel. Fortunately it was just going up so all that happened is the truck fell sideways about 18" and onto its own tires.
I deal with ANSI and ASME construction standards and compliance issues on a daily basis. Trust me when I tell you that the U.S. market is being flooded with non-compliant goods by the containerload. There is nothing protecting you from these products. In fact, the obligation is on the purchaser to know the requirements and purchase only qualifying products.
As far as assuming there's a safety margin engineered into ANY product, the only way you can safely expect that is if the product was built under an audited certification program based on a national consensus standard that includes 3rd party testing and verification.
