I am looking at purchasing an old grocery store. We want to divide it into 4 units. The store has phase 3 electrical. Would we want to change it to phase 1. Half of the building will be a salon with tanning beds. Would it be efficient to change the electrical

There really isn't a reason to make that change. Are you planning on giving each unit it's own panel? Just because the feed is 3 phase there is no reason you can't make the sub panels single phase. It's just a matter of eliminating a leg.

Yes, we want to give each unit their own panel. The electrican we spoke to, wanted to change the feed to 1 feed. The owner of the building could not believe he suggested that along with the heating and cooling person. I think I will be looking for another electrian. Thank you

Good idea. But find an electrician with some building operation experience.

I agree that the 3 phase service entrance should stay, I do not think there is any reason to change to single phase. I also think that each unit should receive the 3 phase.

MB is correct that while the main service is 3 phase, each unit can receive 1 phase by using special metering, each unit may be able to take advantage of the 3 phase. If 3 phase is not needed in any unit, there will still be single phase available in each unit.

If each unit gets a 100 amp service, for example, at single phase they would have 20800 watts available, while a 3 phase 100 amp feeder would have 35984 watts available.

Either way, one thing to keep in mind, assuming this is in the USA, a typical 3 phase service offers 120 and 208 volts. Any equipment, whether 1 or 3 phase must be rated to operate on those voltages.

I mention this as I have run into 240 volt tanning beds, and do not work well on 208.

You do need to find an electrical contractor that has experience dealing with 3 phase.

3 phase 240 is not common although I worked in a building that had it. I also worked in a building that had some 400 V 3 phase stuff because of furnaces from Germany. We also has 208 single and 3 phase and 240 single phase. Had also 277 single phase and 480V 3 phase.

Air conditioning units would benefit with 3 phase. The space size and exactly how you will provide HVAC would play a role.
The tanning guys could get 240 single phase if they needed it from one of the 3 phase legs with a transformer.

In a 480 / 277 system. 480 is used for the HVAC units and 277 is used for lighting. Then 208/120 single phase is used for stuff that "plugs in".

Lots of decisions.