Wholesaling Contracts Buyer undercutting

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Hi I am new to this business, theres a something that has been on my mind...hope some one can help me.  I know there is contracts and things like that yet how do I know if I get a contract and a interested buyer goes to look at the property they like it..... but dont like the price. Can they go directly to the seller and make an offer undercutting me? Or do the contract protect this from happening, and if so aren't the contracts only good for 30-60 days usually. After that cant they easily go and get the property if I was unable to sell it. Or can they talk the seller out of working with me? ...Just curious :)