1. The Secret "Cubic Rate"

If you ship small, heavy items (like a dense book or a metal part), standard weight-based shipping is a ripoff.
The Trick: Use services like PirateShip to access "USPS Priority Mail Cubic." This charges you based on the box size (volume), not weight (up to 20lbs). You can ship a 20lb brick of lead across the country for $9 if the box is small enough.

2. Regional Boxes A & B

USPS Regional Rate boxes are discontinued, BUT the "Cubic" rates mentioned above effectively replaced them.
Rule of Thumb:
• Under 1lb: Always USPS Ground Advantage.
• 1lb - 4lb: USPS Cubic (use your own small box).
• 5lb+: UPS Ground (usually cheaper than USPS for heavy/large items).

3. Insurance Claims: How to Win

Carriers deny 90% of insurance claims by claiming "Insufficient Packaging."
The Defense: Before you seal a high-value box ($100+), take a photo of the item inside the box with the bubble wrap visible. This photo is your "Ace Card." If they deny the claim, upload that photo proving you followed guidelines. They will payout immediately.

4. Understanding "Girth"

For huge items (Golf clubs, Guitar Hero controllers), carriers charge a massive surcharge if "Length + Girth" exceeds 130 inches.
Formula: Length + (2 x Width) + (2 x Height).
If this number hits 130, your shipping cost jumps from $40 to $150. Always measure twice before listing large items.