To that point, another mistake a lot of amateurs make is that they buy expensive things on DigiKey without looking on eBay first.

Amateurs are often poorly positioned to diagnose problems stemming from floor sweepings, parts recovered from e-waste, cheap knockoffs, or outright counterfeits. eBay parts not in those categories are often free samples you can request yourself.

Paying a premium for a new part with predictable characteristics isn't always a mistake.

How else do you suggest they learn? China == cheap education.

Or at the local HAM swapfest.

I think a lot of ham radio gear just uses standard relays for switching RF signals. Apparently they work well enough in many applications.

As long as you are loading with a resonant load then yes, it can work. But as soon as you are in any way reflecting power back on the line or have an impedance mismatch (which will result in reflected power) you're in big trouble.

Another problem is if you use one to switch from say an antenna to a dummy load, you might find that you are leaking quite a bit of power onto the supposedly disconnected antenna link. RF is tricky, especially at higher power levels.

One trick you can use is to use only single contact relays and to bend open the contacts as far as they will go as long as they reliably close again when the relay is energized.

That way you minimize capacitive coupling between the contacts. DC relays are your best bet for a starting point because they already have larger gaps than most AC relays (to inhibit arcing).