Let's say that due to filtering or searching or what have you, there's only one item in the list of products. Should I still show the list for the sake of consistency, or is it more usable to go directly to the product details page?
The system is designed for easy use on a tablet, so there's a sequence of screens where the user can enter information to narrow down the appropriate products for them, some of which are optional and do not appear when there are no options to choose from on them.
Yes, Show the list and from there if the user wants to go to the product he has total control.
The expected behavior when a person searches for a product is to be shown is a list of products and if that step is side stepped and he is directly taken to the product page, he might get confused and wonder what happened.
Here is an example of how Ebay Handles it
The scenario missing here is if the user doesn't find what they are looking for. I would side on keeping it in list form and allowing the user to click if needed. If it's not what they need, they will want to reconfigure the search and filters again.
Both answers before me say 'show the list because it might confuse users'. That's for the most part true because it's convention and keeps the process linear. @Pdxd says that if the product isn't what they are looking for, they can easily change the search query or the filter.
I like to disagree and say show them the item immediately.
A search query that results in just one item is normally a very detailed search query. Like in the example of E-bay with the battery for digital cameras. Such a detailed search query tells you the user know exactly what he or she wants. Directing them directly to this item seems logic and shouldn't cause confusing because they already found what they are looking for.
If it isn't the item they're looking for they can still easily change their search query. All ecommerce websites I know of always have their search bar visibly on screen. Even better is the fact product pages often come with similar products, products other people that looked at that product looked at, products of the same brand, etc. If a search query is so precise it only results in one product and if this product is not the product they're looking for, the search query itself is normally fault for just a small part. There's a big chance the right product will be in those similar products.
