Aquarium Maintenance Service - how to interview

[Ameenah]

I learned the hard way that well-meaning friends should never be offered the task of caring for my tanks and am determined to hire professionals from now on. But how do I know I am really hiring a professional?

There are a couple companies advertising on craigslist regularly but I don't think placing a free ad should be the clincher to hire. 

Should the company use my chemicals? Or do they use their own and bill me for it?
what if a fish gets sick? Do I have to leave instructions and medications to be used?  I cant imagine writing instructions for every possible disease scenario. 
should a company be willing to provide references? What possible questions should I ask their references?
What if my filters breakdown? How will I know if the breakdown was caused by negligence or normal wear and tear?
Is it better to pay a flat per tank fee or pay hourly? When I say 'better' I mean better for my wallet. 
Is it normal to get charged for mileage?
What if fish are missing when I get back?  
Should I hire them a month or so in advance just to watch them work on my tanks?  Or have them watch me? 

Thank you in advance for your tips. 

[devonjohnsgard]

oh, this is a great one for Carl.

[Carl]

My aquarium maintenance company did not charge for chemicals, however medications were a charge if the customer was not a full maintenance client (meaning I came out weekly or bi-weekly and did everything but feed the fish.
I also charged for parts, regardless of whether or not the customer was a full maintenance client or just a cleaning or "call me when you have a problem" client.

I never advertised once for my service other than business card on the aquariums.
It was pretty much all word of mouth including how I got some of my biggest contracts & clients

Carl

[Ameenah]

We do the maintenance ourselves, and do plan to keep on doing it, but we are gone (across the planet) for 3+ months a year and so really need to get the right company lined up ahead of time. Thank you for the tips