What certification do you need to sell electronic device to US market?
If the device is deemed to be information technology equipment (which it may, since it uses Bluetooth) you would be under the '60950' standard - UL 60950, and if you want to cross the border into Canada, CSA C22.2 #60950 (the standards are largely identical, so it makes sense to get both).

Intertek ETL is a US Nationally Recognized Testing Laboratory (NRTL) authorized to test to UL 60950. You could use UL, CSA, TUV, MET or any other NRTL to do the approval - it doesn't have to be Intertek.

The best way to know if the product needs approval is to get an opinion/quotation from an NRTL - they'll tell you what they believe the product needs and how much a certification will cost.