Talking about an average NFT marketplace, perhaps not only on Cardano:
who or what issues or mints NFTs sold/bought on an NFT marketplace?
(1) Is it an NFT marketplace itself mints them? Meaning, participants/users of an NFT marketplace mint NFTs/tokens via an NFT marketplace.
(2) Or participants/users bring their own NFTs/token to an NFT marketplace? The ones bought elsewhere, that is.
(3) Or can it be both? Or either? Depening on a particular marketplace.
Which?
Hello @tiramisu007
If you are asking about secondary market places such as CNFT.IO then users already have NFTs in their wallets that they got from the mint or from other people/markets. To sell NFTs you would:
Minting is different. To mint an asset such as NFT on Cardano you would have to have some Linux knowledge and run a full Cardano node. This would allow you to use Cardano protocol to assemble an asset such as NFT.
For not tech savvy there are services that will mint for you (for a fee). All you have to do is have your assets (such as pictures) ready and know details about your NFT, such as How many? Will you want to change it after minting or is it locked that way for ever? etc… You can see example of NFT minting service here:
Some markets will also offer minting services as well.
On Cardano you can mint CNFT (as in Cardano NFT) and you will need a Cardano wallet to hold these CNFTs. Each blockchain has a different way of doing this.
Hope this answers your question. 
Why would run my own node for minting if I could use a service similar to Infura which provides Cardano node API?
To mint tokens manually on Cardano you have to use custom transactions trough Cardano-cli.
Since Cardano digital assets are not created using smart contracts you have to manually build transactions. This means you need to have a fully synced node. Since Cardano nodes are only about 20 GB it’s way more convenient to just run one then depend on someone else.
Also, not sure what Infura does, but there is no need for having API node service for this. Way easier and free if you just run a node. For example, everyone running a Daedalus wallet on Cardano is already running a full node. Also. I’m not sure if you can submit custom transactions trough Infura node. Didn’t hear of anyone using it yet.
20 GB of disk is ok, but how about RAM? It requires some 30 GB, right? That kind of VPS would cost too much.
How can it ever be free? You pay for a VPS no matter what.
I didn’t say “via infura”. I say - “something similar to infura”.
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It runs okayish with 16 GB.
You do not have to run it on a server. It can just run on your desktop. You can even use the one running inside Daedalus wallet app, anyway.
I don’t have desktop. Even if I had, it’d have to be turned on 24/7, and would use electricity and internet. How would this be free?
Desktop was short for desktop and/or laptop. If you only have a phone, it’s not possible, granted.
And, no, it does not have to run 24/7. You are not running a stake pool. It can be turned on, when you want to do something with it, takes five minutes to sync, and can be turned off afterwards.
As I said: The thing running inside Daedalus is perfectly fine. I’m using it.
Desktop is never a shot for laptop, because laptop kept home 24/7 becomes desktop. I don’t have such a laptop.
If I turned it on for 5 minutes a day, how would my own web projects utilize it at all? I’d have to notify the users, who attempts to pay by Cardano, on my websites: “User… you know… the owner of the wesite isn’t at his laptop now, therefore Cardano node isn’t accesible, and you have to wait for half a day”.
Othwerise, with 5 minutes a day online, what would I use it for?
You never said that you want to provide a service for others minting tokens. …
If you want to mint for yourself, using an own node or even just Daedalus is an option. And running your node for just a couple of minutes a day is a totally normal scenario in that case.
If you want to have a 24/7 service for others, you of course need a 24/7 node to submit the minting transactions to. It could run on your web server (if your hosting provider allows it, there are some that have – rightfully – taken a stance against Bitcoin mining and unfortunately – or also rightfully depending on the viewpoint – thrown other cryptocurrencies under the same bus).
Or, yes, you are right, you could use a Cardano API provider such as Blockfrost. Don’t know Infura, but I suppose it’s a similar service. But then you are dependent on that API provider. And if another SundaeSwap launch like the last couple of days comes along, your API provider becomes hopelessly congested and your service unusable.
@tiramisu007 you may want to start a new topic friend.
Next time instead of asking about the details of unrelated steps out of context ask directly about your project and the problem you are trying to solve. For example: “Can Cardano help fund my project idea?” might be closer to what you are actually looking for.
@DinoDude You might want to stop giving unsolicited advice friend.
Who would mint NFTs on an NFT marketplace if not others?
Have fun trolling then 
You don’t get that your (quite directionless) questions would fit equally well to someone who has an NFT/art project idea and wants to know if it is best to mint on a marketplace, on a third-party minting service or yourself, do you?
So, you want to start a marketplace and/or a minting service? But you have no idea, how this all works? You did not find and at least partly understand the resources that are available? Not even the official documentation Minting NFTs | Cardano Developer Portal? And you don’t have anyone technically more inclined to do it with you, but have to ask in this forum with quite strange objections to the more or less elaborate answers given to you?
I’d say: Let it be! There are established marketplaces and minting services. You won’t be the one starting a better, more successful one.
Re-read my question.
You too 