Girls always see me as the gullible guy or the chump who's easy to use.... How can I change this? Read on....?

Overall I'm a decent looking guy but not a stand out hotty either, which is why I think I fall into this category - the guy who's a good backup plan and easy to use for means of attention and self esteem boosting, but will never be your 1st choice. I don't know why girls treat me this way - I never make myself too available to them, never come across as ''too nice' or ''mr nice guy'' - I just go with the flow and be myself, which is a cool friendly down to earth guy who can be charming at times. However, girls still see me as the gullible guy who's easy to use. The only reason I can think of this is because perhaps It's down to the fact that I am somewhat good looking but not a girls 1st choice guy either, which means they automatically see me as the 2nd choice guy. Who agrees?.... unless someone can tell me what I can do about it?