Sorry about your experience. We had a bad taxi experience in August. We took a taxi to DTD from our resort, CR. The driver took the long way there by the Polynesian resort instead of going straight (there was no traffic). The fee was $24.00 (plus tip). The driver from DTD to CR took the direct route and the fee was $19.00 (plus tip). We didn't say anything to the first driver except I did comment that this is taking an awfully long time.
I wouldn't know the area well enough to know that I'm getting screwed, but if I knew that the ride to get there was $19 and to get back was $24 (I know that is the reverse of your experience) I would tell him that he can consider that $5 he stole from me to be his tip.