How Shops are Cataloged, and How to price your Items Accordingly
How Shops are Cataloged
When you do a search on the shop wizard, you aren't seeing the cheapest prices overall. You are seeing the cheapest prices among a certain group. Shops are grouped by letter, so depending on what your username starts with, these are the groupings, listed below:
A I Q Y 1 9
B J R Z 2
C K S 3
D L T 4
E M U 5
F N V 6
G O W _ 7
H P X 0 8
I'm assuming this is for load balancing, so their servers can handle more searches by only displaying 1/8 of the shop prices at a time. It can also be used to your advantage, especially for cheap items, like scratchcards, codestones, or items that are bought a lot.
My username being theseus51, I'm in the DLT4 group, so with other users with the usernames starting with D, L, T, or the number 4. Because of this, sometimes (not always) I only need to have the cheapest of my group, not all of neoland.
How to price your Items Accordingly
Why should you care about what group you are in? It's so that when you are pricing your items, you have a choice. You can make it the cheapest overall (among 8 groups), or just among your own group. There's benefits to both.
Why would you want to make it the cheapest overall? This is when the item is expensive, like 5,000 or above. People will tend to do a lot of searches, and generally items priced 5,000 and above aren't "impulse items" that people just buy on a whim. This is for expensive items.
Why would you only want to make it the cheapest within your group, not necessarily overall? For the opposite items, the cheaper items that get bought easily. If the item is not that expensive, like a scratchcard or codestone, a lot of times people will just search and refresh a few times and buy whoever has the cheapest item of two or three searches. Their impatience is your financial gain.
Know what group you belong to, and make sure your prices are at least the cheapest in your group. However, sometimes you may not want to be the absolute cheapest . . . and I'll tell you why. Let's look at an example:

As you can see here, you could price your codestone at 4,499 and it'll be the cheapest of this group, if you are in the CKS3 group. But why would you want to give up that extra 100 points? This is especially true if you are selling more than one of that item. What you could do is price your codestone at 4,599, so when someone buys that cheap codestone from karmenwong, yours will be the cheapest.
What you might want to do is buy the codestone from karmenwong, then have two at like 4,580, with it being the cheapest. That way instead of taking 4,499 for one, you will take in 4,580 for both. An extra profit of 160. It won't make you a millionare, but no one tip I share with you will. It's just combined with everything else, this will make you a smarter (and richer) player.
This only really works for items that sell fast, not for expensive plushies or rare morphing potions. For those, people rarely buy them, so you want to have the cheapest overall on the shop wizard.
For map pieces, since you can't search for a specific piece, all you would want to do is make it the cheapest in your group. Even that's hard though, cause not only do you refresh to find the piece, you have to refresh to find your group. There's 9 pieces for each kind of map, and 8 groupings. On average, you might have to search a few dozen times to match the piece and your group to see what others are pricing at.
There's a less than perfect solution, in my Saving Time Pricing the Items in Your Shops section.
Remember though, if an item doesn't sell in 1 minute, don't worry about it. If it doesn't sell after an hour, don't worry about it. Leave it overnight, or for a few hours. Check the shop wizard to see if prices have dropped, or if others have lower ones than yours. You should probably lower your prices if that happens. The next section is about how to save time pricing your items, called Saving Time Pricing the Items in Your Shops.