When To Separate A Block, Old Catalogs, Catalog Price

New to philately and have some questions after getting hooked on this hobby…
I don't know why I assume this, but I expect you just don't break up blocks of stamps. Would there ever be a reason you would? Some examples…
I have 3 US #330 in a vertical strip. All unhinged. Keep them together? Would a dealer be able to sell all 3 at a higher price than 3 separate stamps?

Some blocks have 1-2 stamps with a hinge, 2-3 without. Do you still keep these together? Or separate the hinged from the unhinged?

I have 1992 Scott Catalogs that came with the collection. Recycle? Or is there a market for the used stamps?

And last but not least, when I go to sell my stamps, if I do, I heard that a rule of thumb is to expect about 10% of catalog price if I sell to a dealer. So my 3 #330 would command a price of $37.50 each, using that rule of thumb.
Thanks in advance for your help!

Adding images of the 3 stamps. I've researched a bit, but wanted to share as reference to original post.

The 1992 catalog is so out of date it is unlikely anyone would want it.

That 10% rule of thumb is a dangerous thing. What % you should get will depend on centering and condition of the stamps.

If you are going to sell tp a dealer, don't break up any pairs/strips/blocks. If the dealer wants to break them up after buying them, then they can.

I would ditch the catalogues. I had a full set of 2001 Scotts that were from a Library. I recycled them when they were about 12 years old.

I also would not break up multiples. I haven't seperated stamps in many decades, and that was to mail something.

If these were mine, and I wanted the stamp for my collection, I'd remove one and dispose of the others - this isn't a neat block of four and it doesn't include part of the margin.

I still use old catalogues - I have a 1960s Gibbons Europe that's adequate for my purposes, for example - but the prices are pretty much useless.

Do you mean "dispose" literally? I'm learning about margins now, and understand the importance of centering and margins when determining the grade. I get that there are precise measurements used to determine how large the margins are.
I have one more already in the collection, these were in the catalog of extra stamps(stock I guess) I'm just now getting to.

By "dispose", I mean sell or swap, not incinerate!

There is very little market for older catalogs except to the very few who collect philatelic literature.

To keep a multiple intact or to separate it? It all depends. For the specific case of this strip of 3, it does not really matter. I see no increased demand for a strip rather than 3 singles. The singles would be far more marketable.

Additionally, using the "Antiques Roadshow" mantra ... "Everything is condition, condition, condition", the centering of these three puts them at the lower end of the value scale. While it was not a part of the catalogs in 1992, Scott has more recently introduced a "Stamp Values: U.S. Specialized by Grade", published as a special section within the catalog, and more recently as a separate document. It provides values for various conditions, like the coin hobby had done for decades. Your stamps would grade close to Fine-70 or a bit lower, while the main-listing catalog value you are seeing is for a higher grade. Lastly, while these may be "never hinged" that has a broader meaning that the gum is fully undisturbed by anything else too. I cannot tell the exact gum condition from your image. Bottom line, imo, getting 37.50 for each of these is optimistic.

You have all been extremely helpful. I have a digital subscription to the Scott catalogs, including specialized. It has been very fun going down these rabbit holes, and discovering new information every day. Thank you for the info on the grade of these particular stamps. I didn't mean to imply they were at top end, just providing an example with the 10% ballpark in mind.
Now I can say this was the new thing I learned today. I will recycle the catalogs too.

Maybe I'm not seeing it right, but does that strip you showed have its original gum? I don't see any of the shine one often sees in a pic like that, but nothing is perfect. Hence the question, OG?

If your subscription is for the whole digital set of cats, may we assume your collection includes foreign as well as US? The "rules" for collecting are not entirely uniform for all types of collecting. In this forum our advice is going to tend to focus primarily on collecting US. I mention this because if all you need a catalog to do is help identify an item in general terms, a 1992 cat will be good enough for most of the world, but will not do for collecting US. Certainly not for value, but in more cases than I care to mention not for identification either. So for US the electronic catalog is a much needed corrective. But for general foreign it might be overkill unless you really need it to be up to date. Even then, for some countries the best current information for collectors may be in another catalog entirely.

Its complicated, I know, but you don't have to master it all at once.

I have the entire digital subscription now. I'm getting closer to retirement and found that I enjoy this hobby, so did that before I realized there were other sources out there. It's fine though, I go back and forth. I have also watched a few you tube videos. Next on the list is "how to tell if you have a reproduction".
There is gum and there is shininess with these 3. You can see it in the original before I had to reduce the quality to post here.

There is absolutely a market for used catalogues - If your collection stops at a certain date, later catalogs have a negative value since they only get bigger and bigger. 1971 Scott Catalogs are 2 hardback books. 2000 are probably 10. All of my catalogs have been puchased used.