There are benefits to both platforms. . .
ebay is quicker. List something on ebay and you'll have the money in 2 weeks or less. (ebay has stringent rules about selling computers, phones and other high demand items due to scammers and holds money for those items when sold by new sellers. Trains aren't common scam items and so only higher priced items may result in holds by ebay.)
To sell thru an auction house takes months. I shipped my colelction to Stout in November, and the auction was the next spring. I didn't see money for almost 6 months. He charged 15%. Here in PHX there is only one big auction house that does general merchandise and has online bidding. Their schedule is 8-10 weeks from when you contact them you can drop the items off. They'll be sold 6-10 weeks later. A check is mailed 21 days after the auction. 17 to 23 weeks! They charge 40 percent.
Auction houses sell as is where is. Once they sell it it's done as far as you're concerned. (Actually insurance should cover it once it's dropped off, but theft or loss is such a rare occurence we can ignore it.) If the post office breaks or loses the package the auction house is out, not you. It doesn't matter if the train runs.
ebay can be a nightmare with buyers changing their minds and breaking items so they can be returned. I have this happen about every 600-800 sales. I've had people buy HO trains sealed in the box and then break them because they didn't run on their Lionel track. (One woman actually admitted it in an ebay message and I got to keep all the money and the broken train. Last month, I lost $38 in shipping and had a $40 item become a broken $16 item.)
One problem with auction houses is they sometimes go broke before you get paid. When this happens there are usually complaining sellers for a few months so check the auction house out first.
ebay is a lot of work. It's less work to ship a bunch of trains to one location, than to ship lots of small packages all over.
If the trains are sentimental, an auction house is less emotional than ebay. ebay is like a thousand cuts.
I saw a marx collector last weekend who told me he sold his collection to a guy who did toy buying events. He saw an ad in the paper that a buyer would be at a local hotel for a few days and called. He felt the offer was fair, and the buyer came out and spent 2 long days with a helper packing up the toys.
There are a lot of considerations.
One other point. . . I talked to some people recently who are dropping trains and collectibles with ebay consignment places. About fifty percent including ebay fees is normal. It's better than throwing it out or giving it to Goodwill, but not by much.