How safe is steak tartare?
Butchered meat is generally sterile except on its exterior.  (That doesn't mean parasite- or botulism-free, but it's a start.)

Get the best quality you can from a source you trust.  Keep it at as low a temperature as possible, and don't expose it to warm air for more than the few minutes it takes to prepare.

Cut with a clean knife on a clean surface. Put it right back into the fridge at a very low temp.

Salt and acid, if you use them in your sauce, will provide some anti-bacterial benefits, but this is not foolproof.

People all over the world eat raw meat, but it's best to start with small amounts and see how your system handles it.  If you're a child/pregnant/old/sick, it's much less of a good idea.