Wrong.
Teams might know you're underselling, say, Betts, and make a non-competitive offer. But that just makes it easier for another team to come in with a better offer. And if that one is still low, someone else (or the oginial team) comes back with an even better one. As long as there are mutliple interestd bidders, it will work out.
With some of the mega contracts like Price, it does get tougher, but it still can be done. The Mariners did pretty well unloading Robinson Cano. It's not like they were fighting to keep that contract. And they did so with very likely just one team that was interested...