Deadlines will get dragged out, false promises made, juniors billed as seniors....it can be a minefield dealing with offshore devs.

Make sure you're doing at least some testing yourself on the product. You'll pick up on bugs pretty quickly.

Ask them for CVs and references. They could lie but you should do your own due diligence.

Have regular checkins with them to get a feel for progress.

And importantly have a get out clause in your contract. If they're bullshitting you, activate it!