Many commercial florescent fixtures use shunted lamp holders (tombstones). That means the pins will be shorted together. These will not work with by-pass tubes. You want non-shunted G13 holders
Generally a shunted lamp holder will have only one wire connected to it. Once you take off the fixture’s reflector, check to see if there is one or 2 wires for each side of each holder. Using an ohm meter or continuity tester, make sure each side is independent and not jumpered together. Sometimes you can modify the tombstones and other times it is easier to replace them. Shoplight Solutions stocks new G13 lamp holders.
Below is an example of a shunted tombstone that cannot be repaired.
Below is a repairable holder with a removable shunt.
Here is the repaired tombstone. Note a new hole was carefully drilled in the bottom for the second wire.