National Technical Systems, Inc., which offers testing and certification services, will repurchase 792,266 shares of its common stock from Marvin Hoffman, an executive officer of the company. The purchase will cost $3.9 million, or $4.914 per share and will amount to about 8.6 percent of the company’s common stock. The repurchase will be financed through a $4 million increase in a credit facility with Comerica Bank and First Bank.