I'd just like to say, great job in getting a prospective tenant in your view. Some may not know how much work this can take to do.
Now talking about the dog; that is entirely up to you and what you are willing to deal with.
We just accepted a tenant with a dog, but charged a $150 non-refundable deposite. Pets tend to use the facilities wherever, so carpet replacement, re-seeding the lawn, and scratch marks are some of the damages you can expect when you let a dog into the property. If the damages go further than the $150 can cover, than you can dip into the initial deposite to help cover yourself as well.
Like I said before, it's up to what you are willing to deal with.
On another side, you may find it worth it to let in a dog to ensure you get that golden tenant that every landlord dreams of (you know the ones that pay on time, are easy to work with and take care of the property). If you have other applicants wanting to rent, and they are either better, or just as good, you may choose to select them over the person with the dog.
These are just my thoughts.
I hope this helps