Impact of converting a residential lot to a commercial lot

[Lou Smith]

Does anyone have any heuristics or rules of thumb regarding the price premium (or discount) associated with changing a residential, undeveloped lot to a commercial lot--assuming you can get the zoning change? I'm sure it depends upon what type of commercial entity goes on the property, so let's say the SFH residential lot can be converted to support a small deli or restaurant serving the community. All thoughts and experiences are welcomed.