I bought a house witha 1/4 acre pond 4 years ago. I too, did not know anything about ponding until i made the purchase. I did not ask questions and I ended up either A, learining that ponds arent as clean and neat as i hoped. or B, that my pond is really dirty.
Questions I would ask now...
1. How old is the pond? Mine is 25 years old. you cant walk in it because the muck will swallow you. If you dont want muck then either dig a brand new pond and enjoy it for a few years or get a way bigger pond. 1/4 acre is barely able to sustain an ecosystem.
2. What % of the pond is deeper than 10 feet.
Mine has 2 holes at 15 feet the rest (80%) averages about 5 feet. algae...algae...ALGAE...ALGAE.
If yours is like that..plan on spending 80 bucks a year on weedtrine to kill the coontail and 80 bucks a year to control filamentous algae. (you need both). The dead algae becomes muck. BTW: everyone thinks they can remove algae by hand only once.
3. If the pond is close to the house and there is a septic system make sure they are not mixing. I didnt have that problem but its worth a look. Ask the home owner if you can pour a cup full of pond dye down a drain in the house run some water, wait a day or two and see if the pond turns blue.
4. Make sure there are fish in it. Or at least check for bull frogs. Bull frog tadpoles take 2 years to develop. If you see bull frogs then that is a sign that it dosent freeze.
5. If there is a dam. check for wet spots on the back side. Dont just look. Get back there and probe with a stick.

Thats a few things that i have learned from ponding. There are more but I have to go and dig some algae.