Definately not expert... just to share what I know only.
Miu Miu can be either made in Italy or Turkey. Same as Prada for their leather goods. Usually the initial 1 or 2 seasons would be made in Italy thereafter they will be made in Turkey. So most of the latest seasons of bows, charms or coffers are made in Turkey. Overall, there is no difference in terms of quality.
Authenticate Miu Miu hmmm.... it's always good if you have see an actual one in boutique to know the details of the bag, the interior, the leather (the feel, the look &. the smell), and the weight. The brand of zip Miu Miu or Prada used is the same, most common one is "Lampo". Basicially the leather both brand using is also the same for the same type for example, distressed leather, they bear the same features. For hardware, most of them are in gold color, there were some in silver in past season, nethier of them would be too shiny espcially in picture. The interior lining is usually in fabric, colors depends on the design, and there is a Miu Miu logo plate on the pocket, either sewed in for bigger bags or in retangle shape glued onto the lining for smaller bigs.
A new Miu Miu bag would have a product card and a care care attached inside the bag. If the purchase is directly from Miu Miu boutique, the product card is removed by the SA, such details are actually printed on the receipt. If purcahse from other places like departmental stores or online shops, the product card will be given to customer.
Coffers are most commonly made of calfskin, there are some lambskin. It also havs some weight due the amount of leather used, some people may find it a bit heavy especially the large size. If you are looking for coffer on the internet on ebay or whatever, always put on place like TPF for experts to authenticate and ask for more high resolution pictures. Most of the time you can also spot some difference in fake one when looking in close up. These fakes usually have the failure on the postioning of the coffer lock and front pockets, logos, shiny hardware, matelasse in poor or unnatrual fold, plastic-look-alike "leather", poor workmanship on the knots on the braided handle.
Online shop selling authentic Miu Miu... Net-a-porter, Diabro, Raffaello-network.... there maybe some others.
Hope the info make some sense. Happy shopping and share with us when you find your new baby.