When you are looking at all a seller's wares, under the 'Search' bar it says, "Items for sale from So-and-so",
if you want to be notified about anything a seller may offer be sure there is nothing in the 'Search' bar.
If it is something specific you want, do a search of the seller's items for that.
I'll assume you've set your viewing for Sort by: newly listed.
So, beside where it says "XX results found", you'll see the words Save search. Click it.
You'll be asked to name the search, and be sure the "Email me daily..." box is checked.
Being notified of a new listing is not particularly immediate. Sometimes it takes a whole day or more for that 'new listing' notice to appear in your regular email, and if it is a highly sought-after item, by the time you find out about it someone else has nabbed it.
You can, however, check as regularly as you like if you do it yourself. Under the My eBay at the top of the page scroll down to Saved Searches. Click on your 'Saved Search' and the minute a listing is up for viewing you'll be able to see it.
