The ticket says there is a dilution fee. Is that per sample? What if the concentration of my submitted sample is lower than the recommended range?

The dilution fee is a blanket fee per run. The fee is for dilution in the case that samples are turned in significantly above the range for the assay. On the other hand, if your concentration is lower than the recommended range for a Standard Sensitivity assay, we may email to ask permission to change it to the related High Sensitivity assay.
We will not make dilutions without emailing you first if you have not selected the 'dilution' option on the ticket. (Because of the fee, this is "opt-in". This may mean that your concentration will be inaccurate if your sample is out of range of the assay and you do not request us to dilute it.)
However, because the Fragment Analyzer is a high-throughput instrument, other samples are being analyzed in parallel with yours. If you repeatedly send samples with concentrations so high above the accepted range that they affect the entire assay, we may need to leave a "cushion" of blank spaces around your sample. These spaces will be treated as samples during price calculations.