How is the best way to evaluate a wheel and check for loose spokes or other safety concerns?
With the car on the ground (not jacked up) I grab a spoke on the fellow end and push in and out. Any movement can be felt and often heard, and that's a bad spoke.
Another way is when you drive the car slowly and hear a click - click sound coming from the wheel.
There are probably other ways also.
Whack'em with the plastic handle of a screwdriver and listen for the sound. A good spoke rings and a bad spoke goes "Thud". You can thump'em with your finger, but it gets painful after only a few.
There's several things to look for in addition to those mentioned. Can you post some photos of the wheels you're questioning? Especially close-ups of the spoke ends, both at the hubs and at the felloes.
Like rusty red dust showing anywhere around where wood and steel meet. A definite sign of moisture has gotten in to rust the metal, and motion between the wood and metal scrapes it off and out. The dust does tend to collect near its exit. Often, that dust shows up before you can shake anything enough to find it.
Drive carefully, and enjoy, W2
And when it comes to wheel safety, the old phrase "If in doubt, throw it out" really comes into play!
The brown rust at the felloe end is a good indicator that things are moving. I rap each spoke with the back of a knuckle. Any looseness is clearly audible. In a wooden wheel, the spokes at the bottom of the wheel will be in compression under the load of the car. This will allow you to find loose spokes in the top half with a knuckle rap. Roll the car forward a bit to check the others as they become relaxed.
Hope this helps.
Allan from down under.