The ease of doing certain things depend on the abilities of the person doing them
Answers below:
1.
Allow sorting of products by rating criteria (e.g. if my website rates cars, I will be able to select Ordering by my custom rating criteria (speed, safety etc.) and not just by overall score, title, featured, etc).
This is not possible nor practical based on the way the jReviews tables are currently structured. The ratings are stored in a single field, separated by comma and there's no way to read the individual values for a sorting operation without reading all the records first, which is impractical for large databases. So you would have to have a script that reads the values and writes them to a separate table so you can then run a query using that table. And schedule a cron that runs that script. Not a simple task.
2.
Allow to display all rating criteria and not just overall score in product lists.
Sure, you can do this.
3.
Could the rating calculation be tweaked to include weights based on ranks of users (users will receive ranks in the site forums, etc.). meaning, a rating made by a more 'respectable' user will have a larger effect on the product overall score, than a rating by a newbie. In other words, is there an easy access to the rating calculation and can additional variables be added to it.
Possible, but also not that simple.
You are asking for very custom stuff and you will need to pay someone to do this for you, or do it yoursefl if you decide to buy. #1 especially will require a lot of work.
