Tenant gives deposit to hold and pay first months rent 3 days later

[Phil Blair]

After several texts the tenant agrees to give the deposit that same day and pay the first mos rent Friday, so I agreed to that and they agreed to that, well two days later they decide to back out and demanded to have their security deposit.Well I had to turn down several very potential tenants and many other callers literally like 10-20 people. After talking to a lawyer, he told me to keep all of their texts and the texts of where I had to turn down the other potential tenants. He said that I had a really strong case to keep the security deposit, which I am planning on doing, because the story they gave me is very fishy, they told me they needed to take out a loan to buy a house, I'm like you wouldn't be needing the money to do something like that. But anyhow they started to text me and call me and they think they are not liable because they didn't sign anything, I said there was a contract made, so I said talk to a lawyer or take me to court and I am willing to take this to court and then they demanded their money back and gave me guidelines to give me the money back, so to me they are being very forceful and trying to be aggressive with me, to me there has to be some repercussions for people trying to take advantage of you. I am very new to the landlord/tenant business, so I want to know what to expect when I go to court, what records should I have and what things should I record? Also what has been your experiences with these situations as well?