How to check if the tubes are matched?

Many manufacturers say that it's imperative to acquire tubes for their tube equipment from them and their price is usually 2x or higher the retail value of desired matched pair.

What are the parameters that is realy matter to match for a particular unit if they exist in order to be able to buy tubes from non-manufacturer?

How to check if the tubes are matched with no oscilloscope or tube tester having only multimeter or do I have to acquire one?
Specialty tube dealers like Andy Bauwman know all the test and matching parameters for popular audio products. Not only can he supply perfectly matched sets, but can suggest some NOS brands to push your system performance in the direction you want.

OEM tubes supplied by manufacturers are the same Soviet and Chinese stocks available from a dozen sources. They may be select and matched, but for what they charge there are usually better alternatives.