Mailing Coins In #000 Bubble Mailer

Dave: Now I'm totally confused! I've mailed hundreds myself, and since the last postal increase I've been sending them at .64 cents each. 99.9% have gone through successfully. But I got a message from a PO'd customer today who said it came through with $1.07 postage due. The 000 should receive the standard first class envelope rate and the coin adds rigidity which incurs a 20 cent surchage for a grand total of 64 cents....no?

And, just a side note. The Los Angeles area is a conglomerate of individual cities, each with it's own PO.
I have taken to one clerk in my town, .88
I take the exact same envelope with the exact same coin to one town over, $1.22. I ask the reason for this."this is a parcel." I go back to the other PO and they tell me they overcharged you. I've complained but it does no good.
My PO has one of those kPiosk's where you can do it yourself, ALWAYS 88C under 1 ounce unless I send a Morgan or multiple coins.
Now, less than 1 ounce in a regular size envelope marked "non-machinable", 64C.

Are you sending these out w/o delivery confirmation? My local P.O. requires them to be at least 3/4" thick in order to use delivery confirmation. This also insures they don't go through the machinery. Just curious.

I use them but usually send multiple coins. I don't think I ever sent anything for under $2.

Here's the thing with me: 75% of the coins people win from me on ebay are SINGLE coins with a cost of less than $15.00. Whenever this happens, I toss the coin in a #000 mailer, slap a 64 cent stamp on it, and away it goes. I only bother with tracking or insurance or printing a label from PayPal if the total value is greater than $15.00. Either that is a correct course of action or I'm getting away with murder, because if you look at my DSRs I'm right at 100% for shipping charges, and that wouldn't be the case if all these shipments were showing up with postage due. My contention is that a #000 mailer becomes a PACKAGE only when the thickness exceeds a quarter inch. Until and unless that happens, it's a rigid envelope, and 64 cents is the correct postage. My local postmaster agrees. Unfortunately, once in a great while, the postmaster on the other end of the delivery doesn't see it this way and then I get in trouble.

I just finished addressing a #000 bubble mailer with a 64 cent stamp on it, complete with a coin inside of it, to the Postmaster for zip code 89122. Inside is a letter that basically asks "what, if anything is wrong with this?" and includes a self addressed, post-paid envelope for his/her reply.

Question: when sending out coins in a package and they ask what is inside or if I need to write down what is inside what do you tell them or write down? I don't feel comfortable telling them or writing down 'coins'.