>Hello Craig,
>
>So far there are no contracts. This could sound strange or even stupid but the trust factor is playing a big part in me working with that company.
>
>So because there are no contracts I own the copyright.
>
>I did this as a consultant so I am doing everything (coding, tech support...)
>
>What should I do from here?


No contract could make things ugly in the future. You should consult an attorney that specializes in software law.

Are there any trade secrets that will get out if you sell the software? If not, there is nothing that says you even need to give the client any share. However, if you want to keep them in good graces, 10-15% would be appropriate since you incure all the costs.