This Guide is Most Likely Outdated, as It Hasn't Been Updated in a While. Will Do Research and Make Changes Accordingly.
First thing's first: Introductions. My name is Yuu, and I've played around with the market extensively since I learned about it. In playing around with the Market, I've found some good-and not so good-items that are good money makers. In this Guide, I'll be sharing whatever information I think will be helpful to people who are just starting out on the Market.
The different currencies of the Trove Market:
There are a few currencies offered for your use on the Market, be it buying, selling, or both. Currently, the following resources are available for use as currency on the Market: Flux, Glim, Eye of Q'Bthulhu's, Chaos Chests, Dragon Coins, and Penta-Forged Shadow Souls. Obviously, the easiest things to get on this list are Glim and Eye of Q'Bthulhu's, so the prices for them are naturally higher than if you were to pay with say, Flux.
What sells, and what does not?
The items that sell best on the Player Market (Or just market) are usually not very easy to get. Though, if you have them, and have no use for them, you can make a good amount of Flux/Glim/Whatever currency you choose. If you're in the mood for Glim, and have some leftovers, Eye of Q'Bthulhu's can usually catch around 1k Glim for every 5 you put in, with my general experience. However, I have seen this price go up to 2.5k for 5 Eyes during some periods. If it's Flux you're after, however; 5 Eyes will not get you far. To make even 700 Flux, you need to give either a Pemblock or Meownt. If you have already added these to your collection, along with any and all variations, or just have no want for any of them; Then I heavily recommend you attempt to make some money off these mounts, as some newish players will want to get off their horses ASAP, and upgrade to something with a higher Movement Speed than just 75. Now, I get it; We don't all have Eyes/Tentacles to spare (Tentacles actually sell for quite a bit per one, just so you know. However, they're much, much more rare than Eyes). What else can you sell? Well I have an answer for you: Miner's Troves. Those things you get from mining that drop basically nothing useful to you unless you're strapped for resources? You can sell them for 50 Flux each one at the time of this Guide's inception. So if you just go on a nice mining spree, you can grab a bunch of Miner's Troves and go-to-town on the Marketplace. Naturally, if everyone started selling Miner's Troves, or if the demand for them faded away, the price would go down due to the fact that this game actually has something of a working economy, in that Supply-and-Demand play parts in the shopping of players. If you aren't familiar with the concept of "Supply-and-Demand", it basically means that the more something is needed, the more are produced and the higher the price (Unless there are a lot of sellers...), and the less something is needed, the less is produced and the lower the price. In this case, the next best thing to gather for selling would be Robotic Salvages, giving 10-15 Flux per one, which is the highest rate over all of the normal drops (Not including the drops of the Meownt and Pemblock). However, in order to pull a profit from Robotic Salvages, you would need to gather a good few, requiring a bit of time in the Neon City biome. Unfortunately, the Market is no place for anyone who isn't particularly lucky/selling things that are store items. In order to truly begin making money, one must gather only the finest of drops, including any cache but Miner's Troves and Wooden Troves; Shadow Keys can sell for a bit (400-500 Flux each on a good day), though material grinding can be tedious, and can only be done in the Uber worlds; If you're lucky while fishing and grab a Rare Fish, you can get yourself 1-3k Flux off of that; Or an Enchanted Fish for 1-2.5k Flux (I don't personally understand why the Enchanted ones are worth less than normal Rares... May just be because Enchanted fish are always caught when using the Lady of the Lake fishing rod... The economy is confusing).
Buying on the Marketplace:
Now, we've gone over selling. But how do you know you're getting a good deal when buying? Well, for starters, the Wiki is always a nice place to go to check the current rate of things, however the Wiki is missing quite a few items, so it's hard to get a judgement. One thing you can do is have a look using the search bar to see the prices for others of the same item. Or, you can simply check the "Sort by Unit Price" option on the side, and re-search; This will order them according to the price per one in each set, guaranteeing you the best possible price you can get on the market at that time.
The TL;DR (Or summary of everything in the passage):
Selling: The best things to sell are Mounts and Wings, due to a high demand of them. However, these are hard to get, and aren't always worth the time; So instead try using Eyes or Tentacles or Q'Bthulhu. If those are too hard, get on that mining grind and grab yourself some Miner's Troves for 50 Flux apiece for little effort. If you can't manage mining (Due to low Lasermancy, laziness, or lack of time... I don't know how you live your life.), then just go for the grind for Robotic Salvages. Not only will this get you money, but it will also get you Experience if you aren't level 20, which will also help your Mastery out.
Buying: Buying is less difficult. Just do one of two things, or do both... I won't tell you how to live your life: Check the Wiki for conversion rates, or "Sort by Unit Price" to guarantee best price on the Market at that moment for an item.
Trove's Market can seem a bit complicated at first, due to the fact that any new economy takes a while to adapt to. However, it's not as bad as it seems, and can be likened to real-world economies in many ways. So if you find yourself doing fine in the real-world, you'll do well in Trove. So, this is Yuu, signing off. Feel free to message me if you have any personal questions about the Market place, or anything else I may be able to help with, and thanks for reading.