Additional suggestions:

When rare customers --> When customers, who were rare/infrequent, came into . . .

Local kids were usual guests at the store --> Local kids were the usual customers . . .

It was getting dark outside and street lamps went on --> were coming on.

. . . the newcomer --> this newcomer/new customer

There was some menace in him --> There was something menacing/threatening/frightening in him

The old man coughed up and continued --> The old man coughed and continued ("up" is unnecessary and the reader wonders what was coughed up.)