Founders who've sold or tried to sell — how painful was due diligence?

I'm researching the micro-SaaS acquisition process and keep hearing the same thing: deals stall or die in due diligence because sellers aren't prepared. Missing technical documentation, PII scattered in old exports, no organized data room.
For those who've been through it:

How much time did you spend getting ready for due diligence?
Did you lose a deal or take a lower offer because of documentation gaps?
Would you have paid someone to handle this preparation for you?

Building something in this space and want to understand the real pain before I write a line of code.