Without a hands-on critique using data points I've listed, yer buying blind, particularly if the weapon was offshore built and mail ordered. I've owned and worked on many dozens of flintlock firearms within the span of six decades. If I had to pick one key flintlock gun component it'd be the lock, it's that critical. Any quality USA lock (Chambers, Kibler, L&R, and many more) will hands-down be "best", or at least "made best". L&R offers quality lock replacements for a good many of the offshore flint and percussion guns, and I've used many of their flint locks on both Italian and Spanish firearms.
I recently bought and completed a Pedersoli 2nd Land Pattern Brown Bess kit. The lock tested very good, and that was a pleasant surprise (I've had some marginal locks from them in the past). I used that gun in a recent Rev War reenactment and it worked flawlessly with good sparks on every firing (blanks of course). I got lucky with that lock. Yay me.
From my perspective, the MOST IMPORTANT thing to be aware of with any and all black powder firearms (muzzleloader or cartridge - and I do lots of both) is KEEP THE FIRED POWDER RESIDUE SOFT
as soon as possible. I could write an essay on this topic but it all boils down to that one concept. This applies to bbls, touch hole liners, locks ... also bbls and brass for the cartridge guns.
Anything and everything that's screwed into a black powder firearm's bbl will make those screw threads seem like they're welded after a number of firings, and will be impossible to remove (breech plugs, touch hole vents, snails, bolsters, blow out vents, nipples, etc) unless the bbl is steamed. Therefore I remove at least the breech plug, for a coat of anti-seize grease.
Most folks don't understand black powder firearm maintenance and waste way too much time "cleaning" and wasting money on all manner of "cleaning" concoctions. As long as fired gun BP residue is timely administered, I can clean ANY black powder bbl in less that 15 minutes, typically 5 minutes and with 3 to 6 patches. All that's needed is tepid tap water and some water soluble oil (i.e. - Ballistol, etc). It's not rocket science, it's 18th century practice.