The bottom line is that faculty members have different opinions and have their own expectations of students.
Consider the following tips when reaching out to Faculty about research opportunities:
They want to know that you are really interested in their research and working with them. Do not send a general mass email to several different faculty members.
Look at departments’ websites and what specific faculty members are researching, mention what you have found in your email.
Some faculty members prefer freshman and sophomores who can work in their lab for a long time; others prefer more advance students with a sufficient knowledge base to do the work.
Some faculty members prefer that a student volunteer for a semester before getting credit; others do not want volunteers, because there is no incentive to take the work seriously.