Sounds like $200 is a fair price for an enclosure, 2 sub-woofers (not the best but will sound fine) and an amplifier.
Without unscrewing and removing the sub-woofers you can measure their resistance and this will give you a ball-park estimate of their impedance (2 ohm, 4 ohm, 8 ohm, etc).
It looks like the previous owner has them run in parallel to the amp. From the picture it looks like the speaker cable on the left terminal runs under the amp to the right terminal, then another piece of speaker cable runs from the right terminal to the amp.
If you remove the speaker cable from the amp you can use a multi-meter to measure resistance. You're looking for approximately 2 or 4 ohms.
If you read approximately 1 ohm, then the speakers could be:
- single 2 ohm voice coils
- dual 4 ohm voice coils (most likely)
If you read approximately 2 ohms, then the speakers could be:
- single 4 ohm voice coils (most likely)
- dual 2 ohm voice coils
- dual 8 ohm voice coils
If you read approximately 4 ohms, then the speakers could be:
- single 2 ohm voice coils
- dual 2 ohm voice coils
- dual 4 ohm voice coils
- single 8 ohm voice coils (most likely)
You're looking for 2 ohms to get the "most" out of that amp, but if you read 4 ohms you're fine.
The reality is, it doesn't matter, all that matters is that it sounds fine and you're not overheating the amplifier.
Have the seller put it in a car and let you listen to it. If it sounds like it is worth $200, pay the seller, if it sounds crappy.. offer less or don't buy it.