There are some people who assume that all reptiles and amphibians are the same, probably because they have some similarities. This time, while salamanders and geckos seem similar, they are not. Salamanders are known to be amphibians, while geckos are known to be reptiles. If you would look at them closely, you will start to see the difference. The skin of geckos may vary.
Some of them may be very smooth, and there are also some that would come with some warts. Salamanders will always have smooth skin. Some of them may have skin that is too smooth. They would seem almost slimy, especially from a distance.
Interesting question, I love animals, so sometimes I know random facts about them. So the main difference between them is that salamanders are amphibians, while geckos are reptiles. Also, there is a difference in their skins. Salamanders are smooth and can be slimy (they are like frogs -amphibians- but with a lizard form), geckos skin instead can be smooth or rough, it's impermeable to water. Some people also affirm that the gecko's paws can cause "burns" on the skin, but I never experienced this, so I am not very sure of this.