Star ratings
Aim for 4.5 out of 5 or higher, and look at how many ratings back it up — 4.8 from 300 ratings means far more than 5.0 from 3. Read the actual reviews, including the bad ones; patterns of late shipping or wrong specs matter more than one angry outlier.
Transaction history
This is the number that matters most. Hundreds of completed transactions in your product category means the supplier has actually made and shipped this part, repeatedly. Check that the transactions are for similar products — a thousand phone-case sales don't prove they can build a turbo manifold.
Years on the platform
Longevity is a quiet trust signal. A supplier with 5–8 years on Alibaba has survived on repeat business; scammers rarely last. Combine it with transactions: old account + steady recent sales is the profile you want.
"Verified Supplier" badge
This means a third-party inspection company audited the business — checked the license, visited the premises, confirmed they exist. It's a real filter against pure ghost companies, but it is NOT a quality certification of their parts. Verified + strong transactions = good. Verified alone = just a starting point.
What to ignore
Paid badges, "top ranking" claims, and response-rate stats can all be gamed or bought. Use them as tiebreakers between two already-solid suppliers, never as the reason to trust one.