I've heard of large consulting companies that do a "bait and switch" where the client initially talks to a fantastic technical person prior to signing a contract, then never hears from them again.
Sometimes law firms don't even really disclose who's doing the work, and sometimes in their invoices they'll have a paralegal's initials under the "Atty" column.
This is sometimes true even for very large and reputable law firms.
Every solution architect/ pre sales engineer you talk to before the ink is signed isn't there to do the work, they're there to build trust and confidence that the other folks who can't talk to a client are just as talented.
Also you definitely hear from us again as we bill 4 hours a week or what have you for "Quality Assurance."
It is amazing how many managers I have worked for who don't do that.
Get the contract using great people. Before the ink on the contract is dry, send in hopelessly underqualified staff. By the time the client finds out, their "old" internal resources are long gone, bonuses have been paid out to management for reducing cost etc.
I experienced this first-hand with Cognizant.