snickers,
I weaned on the trailer for 40 years or more - and yes, if you're just running 'em through a salebarn, you get just as much(or as little) as if you'd weaned them properly and given them all the appropriate vaccinations - 'cause the buyers are figuring that they're 'trailer-weaned' and haven't had any vaccinations - and they're likely going to be dealing with some sick calves and some deads.
BUT! It's not the best thing for the calves, or for the next folks on down the line. I no longer send anything but cull cows through any of the local auction barns. I now have a buyer who knows what my cattle are, what they'll do, and knows that my calves have been weaned, vaccinated, and are bunk-broke. They don't have major problems with sick calves or death loss in my calves. Yeah, it costs more, and it's a bit more work, but it's the right thing to do.
I don't consign to the 'certified pre-conditioned' sales, though most of the time, my calves would qualify. But, most of the time, my buyer pays me a little higher than the prices at the CPH sales.