Only agree to a contract of exchange of information that "Guarentee's a percentage of pre-profit sales" so you don't end up paying their TAX
By supplying the "source code " you are in FACT the AUTHOR & anything they do with t is MERELY an UNORIGINAL ARRANGEMENT.
While they are entitled to all mechanical reproduction royalties, you are entitled to ongoing original authors royalties, which means IF they sell it whoever takes it on STILL owes you money from any sales .
While you might not see a cheque for six months its a better deal that KEEPS your NAME on paper & guarentees your not going to see your idea exploited for a one off "allrights " payment.
Besides it will give you the chance to "fund " another project