Ebay has recently made a great number of changes that really do not favor sellers, imho. That said, if he has knowledge of a product, and can source it, there is no reason why he shouldn't try.
It sounds like he's done a little research, which is good. You'd be surprised at the people who don't.
Him having the knowledge you say he does will be a valuable asset.
My recommendation would be this...
for him to not spend any money on any type of course. There are several ebay books on the market, some geared to the absolute beginner. Perhaps you and he could both get the same book, so that you could easily follow along with his progress?
Also, Ebay itself is full of information...enough information that I cannot imagine paying for it.
I'd suggest that he start off doing listings of things he already has and would like to get rid of. That gives him practice without him risking losing money on paid inventory.
He should think ahead, right out of the gate. He needs to pick a username that will be tied in with his product, and he needs to get that registered. Once registered, he needs to buy a few things under this ID. Perhaps things that he would need for shipping, or something of that nature.
Point is, very few people will buy from a seller with zero feedback, and conversely, few people will look at 25 positive feedbacks to see if they were feedbacks as a seller, or feedbacks as a buyer. Not to mention the higher your feedback, the better prices you can command. So getting some numbers under his belt is essential.
Part of the changes recently made were that for some categories, Paypal now will hold funds for 21 days before releasing them to the seller. Doesn't sound like the categories your dad is interested in, but it's something you need to be aware of.
I don't see a reason why he shouldn't give it a try and see what happens. The reality is, selling on ebay and amazon has a lot of similaraties to building galleries or free sites. It's a lot of the same work, over and over and over again. It also requires the ability to take decent pics, write sales text, etc. Some people just aren't cut out to work all day, every day, on a computer, and they don't think about that when they think 'hey, I'm going to sell on ebay'.
Best of luck!