If an automation is resold, does that count as "1 machine" on the license?
>>>> When we use the term "X number of machines" this refers to RTILA STUDIO License activation on X number of computers at one given time. Now when you say "an automation resold" this is not allowed if you mean reselling your Machine allocation as a License to other users. Sub-Licenses of RTILA Studio, or as we call them TEAM URL Activations are to be used only internally with your teams/students/consultants. You cannot resell an RTILA Studio license. See this Doc on how to manage Team Activation URLs: https://rtila.com/docs/manage-license-activation-count/
Now what you can sell are two things:
1- Automations, as in .rtila automation files that you can export and share/sell to your market, we also call this a Template. We do not apply any restriction here. Anyone who receives the .rtila automation file can import it to their own RTILA Studio and edit/modify/run it, even with our Free version. Your client basically gets the source code of that automation and they can change/edit it.
2- Standalone Executables (compiled Bots). For this type of files they can be run without RTILA Studio. If you compile a bot with an RTILA Studio License that does not have reseller rights then it can only run on the computer where it was compiled (self-use only). But if you have Reseller license the executable file will be unlocked and can be run from any computer of your clients without the need for the presence of RTILA Studio on their computer. And the later is what you can sell as you get both the technical "unlocking" of the executable + the right to resell it. Note that for this case your client will not have access to the source code of the automation and will not be able to update/edit the file, for any update they would need to receive a new file version from you.

And if the person/organization that bought it wants to run the tool on multiple machines (say 2 for example), would this then be 2 machines?
>>> If it is an Standalone Executable file compiled by a reseller right license, then the client does not need to have RTILA Studio and they can run the executable file on many computers, unless you put a limitation in your own flow. If it is an Automation file/template, they can run it on our Free version of RTILA Studio or they can purchase a higher tiers.

Do the compiled executables work with MAC, or these are only Windows Executables that are created?
>>> The same Executable config file can work with Mac OS, Windows and Linux meaning your Bots will be compatible with all 3 operating systems.

Finally - what credentials would have to be provided to the customer that bought the automation?
>>> For that specific example the credentials.txt is for the end-user to put their own login/password for the bot to login to their target website. By having the credentials pulled from a local txt file it allows your bot to be credentials agnostic so any user can use it.