Here's the short version of what affects customs clearance:

• FDA rules: Vape hardware that's marketed for nicotine use falls under FDA regulation as an ENDS product. If your device is purely for CBD, it's not a tobacco product, but the hardware itself might still be subject to general product safety rules.
• State laws: Some states have their own restrictions on vaping products, even hardware. Check your state's rules before ordering.
• Labeling: Customs looks for accurate labeling—what's in the box, country of origin, and intended use. Missing info can cause delays.