To be honest, McMaster isn't the cheapest way to go for parts; but their service is second-to-none!
I replaced a cylinder on a customer's machine Friday, and noted a small air leak out a 'port' in the body that was not intended to leak (it's a hole for insertion of a retaining key, not a flow port). It didn't adversely affect the operation, but it wasn't right. So I contacted Mead Fluid Dynamics directly to understand the problem. They allowed as how it could happen, but was so unusual as to raise some red flags.
They wanted the defective cylinder, in order to do a QC check on it and their processes. But I bought it from McMaster, and normally, they would want the return. As is customary, I expected to be billed for the replacement, then credited for it when the dud was processed. I intended to offer a copy of the certificate of receipt by Mead as evidence it had been 'returned' (as it were).
McMaster allowed me to ship the dud to Mead without other 'proof'. They credited me for the bad, shipped the new one, and don't even require any corroboration that Mead got the bad one -- "They'll follow up on their end to ensure this doesn't happen again."
Wow! Where else do you get that sort of service these days?