I'll defer to @Steve Babiak 's expertise in PA, however the sale event is generally the drop dead time/date event you want to beat. 

hi marcus. yes, filters need to be changed often. in fact, i recommend at least once a month, depending on the location of your furnace and cold air return system. that being said, here is my experience and expertise. ( i just competed getting my certification in furnace repair). the purpose of the cold air and fan are to circulate the hot air to the area where heat is needed. but the purpose is also to cool the heat exchanger in the furnace as well. the heat exchanger is a sealed system of pipes that the heat created by the burners heats up. the air from the fan/ cold air return blows passed the heat exchanger to circulate the heat to other areas and to cool the heat exchanger. if the filter is clogged, no air gets past the heat exchanger and consequently, the heat exchanger will overheat and get damaged. i have personally seem the heat exchanger with massive holes in it due entirely to a clogged filter. it is highly unlikely that your heat exchanger inside is full of dirt, but the fan and area around the heat exchanger could be filthy

There has been multiple times where i have had the wholesaler/agent go back to the seller reduce the price and get it at the price i need it and still give the wholesaler their cut.I pay wholesalers for access not their expertise, thats my job.

It's your "opportunity costs" of directing your efforts toward the most efficient use of time and your expertise going to the highest profitable activity.To cost management, look to the cost of hiring out managerial and administrative functions.

Anyoned interested sharing their expertise I would glady buy you dinner.PM me.

They have the knowledge, team, cash, and expertise to clean house,  make repairs, attract higher quality tenants, and raise rents.  

I ran into a deal a little out of my area of expertise , a ware house in washingtion D.C owner does not want to sale but is wiling to do a long term lease.

I on the other hand do have the time to be at the property, but my expertise of construction is very minimal.

Ready to get started on some deals and frankly tap into all the expertise and wisdom that I've seen so freely offered on these forums.  

As I understand, many wholesalers get a bad name, so I want to develop expertise so that I can do it right.