Gratuity

[Biggies]

I have several saved customers at a tennis club. Their cards are on file. Some want us to add 15% gratuity, some 20% and some 25%. I added these in a gratuity tab. It seems the options show up only sometimes after hitting “charge card on file”. Other times it gives a $1, $2, or $3 choice. Is this because the charged amount is smaller (like maybe just for a soda or something)? Is there a way to keep it at the % amounts no matter what the charge amount is? I kinda feel like I set that up but don’t have a CLUE how to change it. 
Anyone? This community has been so helpful. Thank you in advance. 

[Candlestore]

@Biggies ;

You may want to add a service charge and set it by %.  I do not know of a way to add it to specific customers though.  Maybe put a note on the account to add X% Gratuity.   Have different service charges by % and call the item 'Gratuity 15%' for the 15% one etc. for different rates.  

Here is how to add a service charge:

can-i-apply-a-surcharge-to-square-sales 

[Biggies]

Thank you!