The store opened 12 boxes of 20 products, so they put out 20 * 12 = <<20*12=240>>240 product samples.
They had 5 samples left over, so 240 - 5 = <<240-5=235>>235 samples were used.
Each customer could only have one sample, so 235 * 1 = <<235*1=235>>235 customers tried a sample.
#### 235