How can I tell if they are trailer rims?

http://bend.craigslist.org/wto/5354695533.html How can I know before I go check them out?

What is special about trailer rims? Same pattern I need and a common Ford size.

I can tell you this is a fairly common trailer size tire.

Aren't trailer rims weaksauce? Can't imagine trailer rims fly at tech inspection. Nor DOT.

Considering the side-loads placed on them when making tight turns with a tandem axle trailer, they can't be all that weak...

So. Original question remains.

I thought an actual trailer tire was of a higher load spec than a 'P' passenger tire. Ergo an trailer wheel would have to be of a higher load spec, too.

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=219

They mention the higher pressures sometimes needed for trailer tires and wheels. So if a wheel was called a trailer wheel, I'd believe it would be at least as strong as any other vehicle wheel of similar size/construction/material, if not more so. This is probably speculation, however.

I don't care about tires. They are junk anyways. Just the rims. I do occasional autocross but a lot of drifting.

Trailer wheels have to be dot approved to be allowed on the road. Otherwise they are marked not for highway use like race wheels. There is nothing different about a trailer wheel.

Usually trailer wheel have a much larger center hole.

I think it's 3" for the trailer wheel and 2 7/16" for truck wheels. I won't swear to that though.

I believe trailer wheels are always zero offset. If these aren't , then they're likely not trailer wheels.Also, any trailer wheels I've ever bought had a large center hole compared to my car/van wheels. They certainly weren't hub centric.
My current 14",typical white generic set have thick center webs. They've got to be 3/16 thick.