question :if you receive a הזמנה from a so-called בית-דין that charges money for ישיבת בי'ד do you have to respond?

No. the דיינים are פסול לדון since they take money הנוטל שכר לדון דיניו בטילין .

If you owe the guy money,you must pay, אפילו מגלימא דעל כתפיה so the הזמנה is irrelevant.

If you want to know what is the Halacha in a certain situation,go ahead and ask a תלמיד חכם .

Please don't confuse a רב of a Schul or a טוען/דיין with a תלמיד חכם.

The closest choice might be someone who finished Shas with Tosfos or Tur with Bais yosef
five or more times -----it is not necessary to know any תשובות or אחרונים to be a תלמיד חכם

Also ,make sure the one you choose is activley studyimg Torah(described above) RIGHT NOW everyday.He is not involved currently in Kaballa or anything else. Rather,he spends at least 5 hours per day with Shas & Rosh or Tosfos/ Tur & Bais Yosef.

Nowadays it is very hard to find one,so ALWAYS ask the person for references & DO YOUR OWN RESEARCH ask your friend to learn the סוגיא together and become a תלמיד חכם yourself.
We are in dire need of some.