Instead of tape that the clerk can visibly see, use double sided tape to secure the flap.

I mailed my daughter a birthday card. It was large, but not huge and I did not see any caution to put extra postage on it. It came back with, "Postage Due $.20" stamped on it. My husband took it to a different PO to send and was charged another $1.10!!!!!!!!!!!! For a CARD!!!! How can this happen???????? (I know no one has an answer.)

Yes, that has been a rule for many years, BUT ... there is a way around it that I use since some of those envelopes are not the best. Print out your postage online. Then lay the label the long way on the envelope, about an inch from the flap. Now you need to tape your label on, don't you? Use wide packing tape across the label overlapping onto the flap and you're good to go! Alternatively, order the padded ones online. They seem to hold much better.

I had to send out a bunch of small envelopes with 1.5" squares. Went to a P.O., and was told it would cost $1.95 each, as they were not flat enought to fit as an envelope. I took them home, opened them, and repostioned the pieces, and taped the envelopes. The cost was $.95 at another P.O... It made a difference as I was sending 12.

Excellent suggestion! I am going to give that a try!

I guess I am the odd man out, I have an absolutely wonderful clerk at my local PO. She will check the different methods to be sure I am using the best method. She has never complained about the tape, even told me that the actual rules don't say anything about using tape. But I live in a small town and so she is not usually dealing with lines of people so can take the time to help each one. I also do what I can to help her out. She is not allowed to order some of the flat rate items that I can order online. So I order her what she needs and drop it off next time in go by (which is often since it is a half mile from my home).

Probably be a lot less after this kind of news

The local post office told me I could not ship anything in the flat rate envelope if it was no longer flat! So I had to pay the regular postage rate.
So I used my own envelope purchased at Wal-Mart.

The Post Office and UPS transport for each other. (And probably Fedex as well.) The local postmaster told me this.

I went to a post office in Pittsburgh and wanted a flat rate box to send a gift to my granddaughter that was a stuff toy. The clerk said that something like that may be lighter and cheaper if it was in a regular box and pay by the weight not flat rate. He weighed it and it was by about $2.00. I double check all ways before I pay a flat rate.