So, Due Diligence (DD)?
Based on my experience of Infrastructure Outsourcing back in the period 2004-15 when I was performing assurance reviews on bids for one of the major Outsourcing companies, the success of Transition activities (defined as those required to take-on the services from either the previous supplier or in-house) and Transformation (changes from taken-on delivery model to supplier's full delivery model) are almost always underspecified (i.e. wrong) because some or all of the following:-
a) the customer is telling porkies (or at least withholding information) about the scale and scope of the current situation - or may not even know themselves if the process is being managed centrally or at a "Corporate" level
b) the previous supplier is telling porkies and withholding information and/or cooperation - sometimes at the customer's direction - or access to them is forbidden by the customer until very late in the bid/solutioning process (and sometimes only once the contract has been signed)
c) the new supplier's DD's process is inadequate and fails to establish real work volumes and/or deviations from 'norms' (how-so-ever defined - but frequently the 'standard' supplier delivery model)
d) the supplier's bid/solution team deliberately disbelieving evidence from DD activity and solutioning to their solution boilerplate and metrics from post-Transition delivery. (see note 1 below). This is frequently because solution has to be based on metrics and numbers and not real-customer-world.
e) Transition and Transformation Plans that are built on assumptions and not contractually agreed fact (... ker-ching Variation Orders!)
f) There is a major flaw in the new solution model which hasn't been picked up by anybody (possibly because of arrogance - very frequent in my experience - or ignorance by the new supplier) and effectively a new soluition needs to be designed and implemented post service start. (See note 2 below)
g) The new delivery model and design/implementation timescale to achieve it is a fantasy and just simply is not deliverable, and certainly not with the staff / resources available to the new team.
I don't know if things have changed over the past ten years, or Business Processing Outsourcing differs from Infrastructure Outsourcing (but my couple of examples of being involved in bids covering both suggests not).
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Note 1: One of the final bids I was involved with had widely distributed customer servers with broadcast-TV receiving hardware in many countries to capture live TV in that region for analysis of local adversing patterns. Proposed solution was for these to be centralised into major datacentres (i.e. one or two covering entire continents) and eventually virtualised either private or public cloud solution. Costs were of course based on the standard model for basic and standard hardware models. No amount of pointing this out in solution reviews that that this wouldn't meet the customer's obvious need was listened to. I never knew this actualy worked out in practice as I took redundancy and retired before the account Transformation was complete. One solution fits all - NOT!
Note 2: (Not a deal I was involved in reviewing, but one I subsequently was involved in reviewing in delivery and at renewal) A global infrastructure outsourcing deal in the Pharmaceutical Industry was signed before the supplier discovered and understood the constraints and additional working required to meet FDA/GxP requirements - no-one on the bid or solution design team had ever been exposed to this industry before. Cure - almost total re-solution at supplier cost (involving staff from other areas of the company, external experts and transferred resources (e.g. TUPE) from the customer that the origional solution would have removed ASAP) and delay of 2-3 years in moving to supplier delivery model (which was significantly more expensive to deliver than the contracted one).