The simplest check, ask someone who is connected to the network already.
If you have never connected before, and don't know anyone who is on the network, then it's more complicated..

(although you could say that downloading the software is a risk in itself - is it legit or hacked, and any legit version would include some checkpoints)
And if I have a majority of fake nodes broadcasting my fake chain to those who wish to sync, the chances of asking my fake node is greater than 50%, isn't it?
The point about checkpoints is that when your protocol depends upon them for security purposes, you might as well just throw the whole thing in the bin and use a 100% centralised service, which will be exactly as secure and a lot faster, cheaper and easier to use.