I'm with BSG. It is harder and more time consuming to do a compromised job with sub-par tracks or stems.
The only difference is worrying about putting my name on half assed stuff. If the artist is going to give you bad tracks, or paint you into a corner, then chances are, not many people will ever hear it.
Also, if you do enough good work, that will speak for itself. If you are known for your good work, anyone who hears the bad stuff will assume it's the band.
And then there is the fact that what others think is bad (music) is just personal opinion.
That being said, I work with quite a few genres. Most all original except for the occasional cover tune. But 99% of the time it is all original instruments recorded by either myself or friends. I got a bunch of extremely talented guys on my friends list...
The last cover tune I did with a 'purchased' backing track was for a girl who wanted to sing a song at here grandma's funeral. Well worth my time and free to her. That was a Melodyne moment and worth every penny...
Oh yeah, and I forgot about the rapper guys... They are good tho...
Anyway, most of what I do is record full band records from drums to finish mix. Sometimes mastering though I like it better when they pay another to do that. I won't take the time to describe why.
I occasionally do free work for members here. But only when I find something I feel I can help with.
Some times just a one off mix for a member in need. If I feel I like it and give a shit personally, I will offer to mix. A couple of times, they actually turned out to be semi successful collaborations/releases in other countries over the years. No Grammy's here by any means, but some great product and learning experience for myself as well as meeting people from other countries.
One such member that I mixed/produced/mastered a record for 4 years ago, came to US from Germany to see the US with his brother. We spent 3 days touring a land he and his brother had only seen in movies. I learned more from them in three days about the world than I had in 40 years. It was fucking awesome! I would not have had that experience if it were not for this forum and my being here to offer help to someone asking.
So for myself, I take offers for work like I choose raw meat at the store. If it looks good and fresh and I know what marinade works for me and may be tasty for others? Well maybe I take on the cooking/mixing of the genre of product.
If it does not seem like a good mix of spices, I would surely not charge someone for me to 'Google How To Mix This Record'. That would just be bullshit and not cool.
To often 'one time' posters come here for help, only to never return to help others. That has always made me wonder why I am here. Then I see my daughter...
Is it more about 'if' what I feel I can do to help someone who has a real need for help, knows what they actually need? It may be...