DM Screen yes, it is a 1st print.
Is that Tape across the right edge?
If so, then maybe $35-$40 if someone wants one badly.
Also do not have pics of inside.
Other than the tape it looks really nice...
so.... Fine + almost VF
Without that tape... close to NM I think... NICE...

PHB with the yellow endpapers?
VG +

MM 1st hardcover... Hard for me to say as I have one listed right now.
VG +

DMG
VG

Deities & Demigods with Cthulhu: 1st Printing
Fine to VF -    has edge wear and rounded corners, if no writting and NICE inside, VF would not be outrageous IMO

More photos added re screen.

Are you based in the UK or in the US?
Your listings are confusing as they are US listings but your Acaeum ID indicates that you're in the UK.
For UK listings, most of your prices are at least 50% higher than they should be, presuming you're wanting to sell stuff and create a customer base. But I realise you may be trying to establish yourself as a prestige outlet and pricing yourself into that bracket.

Lucky you. You may be able to hit the Con's if you have the time. Especially NRTRPGCon (North Texas RPG Con). There are a lot of us in the UK who wish we could attend sometime.

As regards selling items, the best way unless you are absolutely attached to a particular item for some reason, is to list with decent photos at 99p and just let the market dictate the value. So long as your photos are good, your likely to get +/-15% of each item's real current value, and over a spread of 100 or so items, you'll pretty much be getting what they are worth. They are also far more likely to sell rather than telling people how much they should be bidding for your goods. As I say, if you're building a shop and want to establish a certain prestige and clientelle, you're doing the right thing, but should be weeding out the mundane and the less than perfect, but if you're trying to sell, the prices are above what most people would be willing to pay.

A big mistake a lot of newbies to eBay make, is looking at other people's asking prices and then at Amazon to try to assess what their price should be. What you should be looking at is previous sale prices and what buyers are willing to pay for an item and not what some fanatsist thinks he might get for his books. It's hard with some things, but then for every week or month you fail to sell, that's a whole new set of listing fees you've written off against any eventual sale price. It's tough sometimes, but trusting the free market is a fairly robust tactic.