I'm seeking objective answers, so that this is not closed as subjective. Question may be moved to a different site if required.
What is the difference between AWS Marketplace and
sudo apt-get install, and how do I decide to choose one over the other?
I noted that Amazon AWS has a marketplace with ready-to-deploy offerings like LAMP Stack from Bitnami. But tutorials often instruct you to create a blank EC2 instance, SSH into it, and manually install software using commands like sudo apt-get install lamp-server^.
Are they the same? What are the advantages and disadvantages of each method?
If I get an offering from the AWS Marketplace, can I install other software to the same EC2 instance using either method? If there's a paid offering from AWS Marketplace that I used sudo apt-get to install, will Amazon charge me? (They should, right? Or that will be a big loophole many will exploit.)
AWS Marketplace allows you as a developer or company to create a re-usable AMI pre-packaged with an installation of software. This installation can then be used by end users, either paid for, or free.
As a user, it allows you to easily provision servers with software pre-installed. A very common use case is to allow people to license software hourly rather than upfront or monthly (hence fitting into the elasticity of AWS). For instance, if I have Software X which I need a baseline of 10 servers, I may pay the developer for a perpetual licence for 10 - however at peaks I'll use AWS Marketplace and license by the hour as necessary
Are they the same? What are the advantages and disadvantages of each method?
Often software pre-installed onto an AMI will come pre-configured - so for instance the Bitnami AMIs allow you to easily deploy Wordpress fully pre-configured.
This does, however, mean that the initial configuration choices that were made by a third party can impact (positively or negatively) your application. Subsequently you may choose to install and configure your own applications from scratch - possibly even creating an AMI yourself which you can re-use for further deployments of that application
If there's a paid offering from AWS Marketplace that I used sudo apt-get to install, will Amazon charge me? (They should, right? Or that will be a big loophole many will exploit.)
Amazon will not charge you, no. If for instance there was a paid Wordpress AMI, and you then created an EC2 instance, installed Apache, MySQL, PHP, and Wordpress -- Amazon would not charge you anything additional.