Is it wise to buy a used DSLR from Amazon?

I'm planning to get a DSLR, Canon 5d mark 3 used or nikon d800 (new or used).
for example on Amazon, the seller wants to sell his Nikon d800 for 2400$ only. He wrote:
Used - Like New
Perfect condition, no scratches, no problems. Only used once indoors, took about 250 shots. Comes with all original accessories, manuals, packaging, box, etc. Includes unused warranty card. Only selling because I decided to stick with my d700.

i live in other continent, He's from the usa. How can i make sure that the DSLR is in perfect condition.

PS: i'm planning to get a used DSLR to save money for the (lenses, bag, uv filter, flash, cleaning kit,… )

my budget is 3600$ and i'm trying to assemble the perfect kit before buying all the items.

any suggestion? (advice for buying from a trustful resource, and cheap… )
Do i get all the items from one seller? (to save up for the customs and taxes?

My main shooting purpose:
making short films, shooting in weddings (i won't be the main shooter,), shooting nature, and some low light situations…

When you buy from the Amazon marketplace, you are buying from an independent company or person. So the traditional caveat for buying used on eBay would apply here. I have found though that often, marketplace sellers will "attach" their item to an advertised item that may or may not be exactly the same - so you have to read the fine print on the description, and also if not sure, ask the seller for an explicit description.

For instance, I have seen used lenses for sale on Amazon. Sometimes they might have a few scratches and dings, or missing parts that you won't know about unless you dig into the descriptions. Once I saw a lens that was not even the same exact model, but a consumer-grade version (the Amazon page was for a f/2.8, while the seller had a f/3.5~5.6).

So make sure you get the exact description of what you are wanting to buy.

The good thing is that Amazon will stick with you should there be any issues.

The bad thing is the Nikon warranty will not transfer, if that is important to you.