In 2015-2016, I sold a collection for a good friend's family after he passed.
You can try the auction houses, but depending on how much of a backlog they have, it could be a year or longer before they can get to selling the stuff, if they are even able to sell it all at once. I know I spoke to one auctioneer at the time and he said he could not get to any new items for 12 months, and he was having an auction once a month at the time.
If you decide to sell it yourself, like I did, plan on the process taking a while. You also have to educate yourself on what things should sell for, because as others have said, you have to price it appropriately. I also learned that one should consider all offers and accept many, especially if you have a large collection to sell. I know I turned down an early offer on a piece of Modern Lionel at the beginning of the process, because I was lead to believe it should go for more. Many months later, I accepted a lower price on the item, from the same individual.
The collection I sold was a mix of pre-war, post-war, and modern, and books, etc., all in various conditions. I am lucky as I live in the Chicago area and the Great Midwest Train Show is held monthly at the Dupage County Fairgrounds, so I had a regular show to sell at. Prior to going to any show, I networked with friends and people I knew through trains and sold several things. I also took certain items to the TCA show in York, PA, both in the fall of 2015 and the spring of 2016.
Networking at the beginning of the process and the York show proved great for selling some of the more collectible items at the beginning of the process and I sold about 20% of the net proceeds through networking and 33% of the net proceeds of the collection during the York week, as I sold at one of the early shows and the main show. At some point I was left with a lot of very mediocre trains and at one of the local Great Midwest Train Shows, I had a $5 and $10 sale. I unloaded over $1,100 of stuff that day, all at $5 or $10 per item. Selling the books was a process, as some were relatively desirable and sold for decent money, but others were eventually priced at 3 for $5. When I finally got near the end of the books and they were not selling any more, I donated about a box of books and other miscellaneous items to Goodwill, as they are heavy to drag around, especially when not selling.
I ended up selling the collection over a period of 12 months.
That being said, I am not sure I would do it in today's market, which is significantly different than it was only 3 - 4 years ago.
