Wow - I'd say to avoid that LBS if they can't answer that.
Although I'm more of an IGH guy, the 1x conventional drivetrain has alot of appeal to me. That said, my $.02 would be to go the IGH route.

To convert to a 1x the process is pretty straightforward, and you may even be able to use the crank that came on the bike (remove the chainrings and use the desired size where the middle ring mounts) - spacers may be necessary depending on the chain line. Chain line would be the main issue, and several companies manufacture "chain keepers" that prevent the chain from coming off of the chainring when at the extremes.

Many bike shops will do swaps for you, so you might work a deal with a SS crankset in lieu of the one that is specc'ed for the bike. Depending on the model, they may give you a partial credit for the value of the original crank/shifter/derailluer, or they may simply give you the crank (to use or sell) and you'll essentially be buying the bike + new crank/chain keeper. some shops are more flexible than others.

If it were me, I'd just buy the bike, buy the single chainring stuff and do the swap myself, then sell the other stuff on craigslist or Ebay.

Regardless, the conversion will cost some money. I would guess the parts would be anywhere between $50-75 for a basic chainring/keeper/spacer setup, to $150 or so for a modest SS crank/keeper.

I'm sure that folks who have actually used these setups can give you much better guidance, but I'd say go for it.