Before you read a service contract, write down the breakdowns you have actually had with the item or with items like it. A contract is a tool for one kind of expense. The first job is to find out whether your household has that expense at all.
Sort the repairs into piles
Gather the repair invoices, notes, and receipts for the item over the time you have owned it. Sort each event into one of three piles. The routine pile holds small, expected work such as filters, belts, bulbs, and cleaning. The occasional pile holds parts that wear out on a pattern you can see, such as a pump or a starter. The major pile holds the single failure that would be hard to pay for out of savings without strain.
The piles matter because a service contract is usually written around failures that happen after the maker's own warranty has ended. If your records show only routine work, a contract may add cost without answering a real problem. If the major pile has an entry, you have the kind of problem a contract is designed to address, but only for the parts and failures it names.
Check the major pile against the contract
For each entry in the major pile, ask whether that failure is one the contract lists as covered. Read the covered list itself, not the summary on the sales sheet. Note whether the failure happened to an item of the same age, mileage, or use level as yours, because many contracts set limits on when coverage begins and ends.
Questions to take into the sale
Ask the seller to show you the page in the signed contract where the major failure appears. Ask whether the item must be inspected or in working order at the time of purchase. Ask what the contract says happens to coverage if the item sits unused for a long stretch. Write each answer down next to its page reference.
What this does not tell you
Sorting your repairs shows you what you have already faced. It does not tell you what any contract will pay, and it does not rank one contract above another. The state pages on this site list the rules and the roster for each state. The contract itself controls what is covered.