They're as accurate as any 70 year old milsurp that went through a World War...
Which is to say, it really depends on the one you get. Bore condition matters, how tight it is in the stock, good ammo matters...
Mine, I'm quite happy with. I get under 5" groups very consistently with 40 year old surplus ammo - which is all I'd expect from any rifle that old, with old ammo, my old eyes, and open sights.
The SVT has a bit of a learning curve in terms of cleaning and maintenance, but there's tons of good advice (and a sticky) on that subject, so no need to panic.
And they're just a ###y beast of a rifle.
Don't expect it to be your 100% reliable, super accurate, SHTF DMR rifle, and you'll be happy with it. Expect it to be a gorgeous piece of history you can take to the range just for the joy of hearing it roar.
And speaking of roar - invest in upgraded hearing protection. Just saying.