I've also looked into smart locks but I wouldn't be able to change the codes remotely since I'm not paying for the tenant's internet.The other part is dealing with rekeying the property. 

Reach out to me if you're in need of a realtor, painter, tile renewal pro, cleaner, lock-smith, handyman, or property management company.

Can we just get a locksmith to open the door?  

Good cleaning teams and handman are a MUST along with a solid electrician, plumber, locksmith, ect.

For example, most of the time you can't charge a tenant for re-keying the place which is something that should be done with every turn.

Locksmith- Knauss and sons

A locksmith can let your realtor in with proper notice. 

As they have moved out, we have rekeyed the entire property.

If it's obviously vacant (no utilities, nothing inside the house), then you may just want to document that (we usually take photos/video) and move forward with your final accounting and rekey.

@Randy VirdenI invested in good lock sets from a locksmith, not cheap sets from the likes of Home Depot made to a price.