If the wood was "green" (fresh, not dried)
Well, after looking again, title of this thread says "Fresh Cut Centerpieces", so apparently they are green. For the time and labor to "fix" the mold problem, Jamie can go out to the local tree guy and have them cut some slices probably for free or for cheap, allow to dry and buy a belt sander from the local pawn shop and sand them smooth.
Centerpieces would be somewhat large, so checking may likely be a concern for Jamie, also. If they do check badly, he/she can saw through the crack (removing the crack) and glue the halves back together. More than one potential problem, here, and likely more trouble/chagrin for Jamie in his/her effort to have to correct someone else's screw up.
But yeah, contact the vender and try to have them remedy the problem. The cause, on several counts, is totally on their end.
Sonny