My concern would be about Marek's disease. If their chickens had it, the virus lives for a year, at least, in dander and feathers on the property. Do ask about any issues they might have had with their birds; any information will be helpful.
For new chicks next year, having them vaccinated against Marek's disease, and isolated from your soil and coop area for two weeks, will give good protection against the tumors that kill Marek's infected birds. And feeding amprolium medicated chick starter until after they have been on your ground for a couple of weeks will likely protect them from getting sick if there is a lot of coccidia out there.
Your birds might be fine without doing either, but it would be safer to be proactive protecting them.
If it's been more than a couple of years since chickens were there, you will be less likely to have Marek's disease present. Coccidia might be anywhere, and time will tell you if there's a problem with your soil, or not.
Mary