Around here, these are known as a Contracts for Deed. Ideally, you need to verify the terms...down-payment, rate, contract term, balloon payment, etc. These can help gauge cash equivalency.
The critical aspect is to ensure whether or not the contract terms affected the price. Often, even when the terms suggest an adjustment for cash equivalency is warranted, comparison to cash or conventionally financed sales do not support that.
These become more common when conventional financing becomes less attractive or less "available," but in some markets, are always in the mix. Like any other sale, if you put them in a grid and they say the same thing as all the other data, your fine. But when one is an outlier, the reasons causing that should be understood.