How binding are offer letters?

I am(hopefully) about to get an offer for a year contract. However, I just heard today from a company that is looking to fill a permanent full time position and I’m going to talk with them tomorrow.

Now, the thing is that the full time job isn’t a sure thing by any stretch so I don’t feel comfortable turning down the contract position but I know the contract position will be, at most, 14 months and the company doesn’t have a great reputation so I don’t want to shut down the potential for a full time job.

With that background, how bad would it be if I accepted the contract offer, then if I get offered the full time position accept that one instead?

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