TSLA's Price/Sales ratio has been sliced in half since the first time the stock price was as these levels (Q1 2014). As a bear, what Price/Sales would you find reasonable for a company continuing to grow sales 50% YOY
Not to nitpick, but this is a bit exaggerated. Your statement led me to check on these a bit.
Quarter ****** Revenue -- Share count
Q1 2014 letter: 620.5 M ---- 123.5M
Q1 2016 letter: 1147 M ---- 133M
Q2 2016 : < 1147 M (exp) --- 147.2M
Since the SP is same now as around April 2014, let's just say it is 216. Then, P/S after Q1 of 2014 was 43. P/S for Q2 will be 27.72. Not quite half as you said, but close (64%).
Also, with 50% sales growth each year, in 2 years, revenues should have been 2.25 times of Q1'14 revenue. But it is only 1.84 times, implying around 35% yoy growth.
Edit: OK, I made a mistake. I only took quarterly sales (not annual), so P/S is not correct, but the ratio should be okay. To get annual P/S, divide by 4.