It's not about the Jays being around .500, it's about how far behind they are of a playoff spot that should determine whether they buy or sell. The Jays right now are 7.5 back of the 2nd WC, 8.5 back of the 1st WC, and 9 back of the division. A nice run over the next few weeks should shave those games back a bit, but unless the team is within 5 games of a playoff spot, I wouldn't say buying is guaranteed.
With that said, sellers at the deadline recently are not getting great hauls, so could always keep Semien, Ray, etc, and either try to extend them or in Semien's case a QO.