Now one of my good home school coach friends told me once that the eligibility rule for home school was for players to leave their wives and kids at home ...
But yes, eligibility violations occur in all leagues, all sports. You should expect if a school (or home school organization) is a member of a league, they will comply with the rules of that league. If you're not a member of that league, it's in your rights (and obligation to your own school) to ask that your opponent share the eligibility rules of their league with you.
If they are not a member of a league, well, it is "buyer beware." But if you trust and respect the word of your opponent, that should be good. I'd still ask for their eligibility rules and specifically ask (especially for home school groups) how they confirm that a team member is eligible (ie, not enrolled at another school). As Ronald Reagan used to say, "trust but verify."
The generally accepted rules of eligibility are:
1. Enrolled in the school where they are participating and eligible under school rules (ie, eligible under academic rules, not under disciplinary action such as school suspension, alternative school, etc.). (TAPPS defines enrollment as being withdrawn from their previous school if a transfer is involved as there have been some instances of a kid not withdrawing from one school and enrolling in another school.)
2. No more than four years passed since enrolled in grade 9 and have not graduated from high school.
3. No older than 19 as of September 1 of current year.
4. Not participated as a professional athlete in the sport (Maintained "amatuer status").
5. Met any other requirements of the school's league (required transfer paperwork, residency or parental issues -- for example TAPPS requires approval if a student lives with anyone other than their parents or legal guardian or foreign students).
Folks, I as an Athletic Director, would expect to be called on the carpet by my administration (not to say anything about parents) if I allowed any of my sports teams to participate against schools or organizations that did not follow these types of rules. The personal liability (or at least the effect to my professional career as an AD) that I would incur by allowing, for example, my football team to take on a team of 20-year-old all-stars or local 5A "last cuts" that drifted over to a pick-up church team isn't something I would want to have happen -- not to say the possible injuries that could occur to my own team's kids.
Ask the questions. Hopefully it's a formality, but you've done your job.