function doPost(e) {
  var data = e.postData.contents;
  var diamond = JSON.parse(data).diamond;
  var brandProduct = JSON.parse(data).brandProduct;
  // Process appraisal logic here
  var result = "Appraisal result: " + diamond.carat + " carat diamond and " + brandProduct.brand_name + " brand product";
  return ContentService.createTextOutput(result).setMimeType(ContentService.MimeType.TEXT);
}