If you and they came together and examined the project and to that you said for this amount of money I could do this, and to that your offer they said yes please and then asked if you can do it on ____ date until date _____ and if you said yes I can do that and they said good lets do it. That is a contract.
The only issue is, with out it in writing a court will have to decide what was and was not agreed to.
Text and messages can help here.
What the court will know is the following.
You are not a charity and yes someone did the work.
The second person will have to show who did it and what that cost, if you staged the place, that normally includes rented furniture or even plants, that would be in your name.
With that established, it seems unlikely that you would have the original discussion and provided furniture and plants if you were not retained to do the job.
Its easy to lie to each other but if this landed in a court, that requires a completely bigger set of balls to lie to.