A lot is a bet. The only way to make it a sensible one is to be clear about what is known.
The questions
"How much of this have you been through?" Checked and listed, partly checked, or not opened at all. Three different purchases, and the answer should move your number more than the contents do. Non-answer: "There's some good stuff in there."
"Can you lay it out?" A lot shown closed is a lot nobody should bid on.
"How many pieces, roughly, and what does it weigh?" The count tells you what you are getting; the weight tells you what delivery will cost.
"What are you not guaranteeing?" Electricals untested, chips unchecked, nothing identified. A seller who says this plainly is the one to bid with.
"Can you show me that item specifically?" Sellers expect it. A refusal without a reason should lower your bid.
"Is it collection or delivery?" For most lots, collection — and the terms are agreed before you bid. How pickup works.
The discipline that makes this category enjoyable
Decide what the visible contents are worth to you, and bid that. Treat anything underneath as a bonus rather than a reason. People who bid on what might be in a lot lose money on average.
What protection covers
A lot materially not as shown — a different box, far fewer items than stated, damage described as absent: seven days from delivery. A lot honestly sold as unsorted that disappointed is not.
Questions people ask
Why would a seller not check?
Time, volume, or because unsorted is worth more to the right buyer. All legitimate when said.
What if something restricted turns up?
It should not have been listed. Report it.
Can I ask for the weight before bidding?
Yes, and you should if it is being posted.
More: buying lots, what one is worth.