Craigslist isn't like ebay, and I wouldn't commit to buy hardware without seeing it up close and personal anyway. But what I have done in the past is contacted the seller and told them it was conditional on the point that everything was in servicable condition.
Thats when you can negociate prices down due to defects or stuff tanking more work that you thought etc.
If you don't like the deal, you can walk away.. Don't give them the cash.
Most tanks are for Pick up only so it works out.