What happens if the sample is lost while being held by a third party as agreed upon by the parties involved in the agreement? 
The seller will have the final say on whether the specified thing being sold is in conformity, unless the purchaser can prove otherwise. However, if the goods are specified by type or are not agreed to be the thing contracted for, the purchaser will have the final say on whether the property is in conformity, unless the other party can prove otherwise.