Perhaps a few facts will be helpful.
The Agreement by which Mike transferred ownership of the Diary to Robert Smith (Smith Gryphon Ltd) for the sum of £1 was signed on 24 March 1993, having been drawn up the previous day. According to Inside Story (p. 29), Mike had already told Smith before this that he wanted to sell the Diary to him.
Despite the Guardian of 24 March 1993 reporting that Feldman and Smith believed that the Diary "had remained where it was found untouched for 100 years", the first newspaper mention of the Diary possibly having been found in Maybrick's house was not until a Liverpool Post article of 23 April 1993, almost a month after the Agreement was signed.
It would seem to be rather unlikely, therefore, that newspapers speculating that the Diary came out of Maybrick's house had any part to play in Mike's decision to sign the Agreement.