Locking partially depends on how you design your application. Many
Access apps suffer from performance degration after a straight port
because Jet is able to perform caching on the local machine, an
ability you don't have when all calls go over the wire. Also, pay
attention to how the database is designed and normalized. Concurrency
suffers when 2 users attempt to manipulate data on the same row at the
same time, leading to blocking and deadlocking issues. I'd recommend
searching on the phrase "SQL Server isolation levels" and reading up
on the subject. Your customer is right to be concerned.

-Mary

Why? There are good reasons to migrate but does the customer have
those good reasons?

Tony