What is the value of a 1957 G US one dollar silver certificate?

Answer 1

There's no "1957G" silver certificate. The highest series letter was B. "G" may be part of the serial number or a plate indicator.

Regardless of the series letter, the value depends substantially upon the condition of the note. In circulated condition with even minor damage, it might not be worth any more than face value. In uncirculated condition, they can fetch as much as $6 to $8; notes that have been graded and sleeved by a recognized currency grading organization, such as PMG, can be more valuable than an identical, ungraded specimen.

"Star notes" (bills that have the initial letter in the serial number replaced by a star) and notes with particularly interesting serial numbers (such as palindromes, sequences, very low numbers, or numbers consisting of all one number) can command much higher prices, especially when the condition of the note is high.