Have you checked the answer here http://www.responsible-volunteering.com/question/love-volunteers-reliability/
 
Please also ask for advice here https://www.facebook.com/groups/454436357989887/ . The group is full of industrie profesionalls and former and future volunteers.
To understand How voluntourism works, this article might be helpful http://www.responsible-volunteering.com/2016/10/voluntourism-companies-outsourcing/ .
Please let us know about your volunteer experience!
 
Sebastian