would it be safe to sell things and meet people inside a Walmart?

So you want to be a Walmart cashier?

I suppose it's fairly safe.

Or you're wanting to use Walmart for a purpose other than what it is intended?

Join a flea market.

You can’t sell stuff inside Walmart but outside Walmart parking is a meeting area

Local police station...just the lobby. Any scammer or criminal wont show...and you wont get robbed.

Sell at flea markets or tag sales in front of your home. Stores do not permit Seller’s to set up selling within their store.

You can only 'sell things' inside Walmart if you work for that company. Some 'community' groups can sell things outside of Walmart at folding tables, such as Teen Challenge, but they have to have permission.

where would be a good place then?