So ive never graded cards but for months im learning about it, i have several questions thats bothering me. They are general questions, ik its different every time but im asking for someone who graded hundreds of times for a overall standart.
1.Are the 4 defining things:
Surface (centering) edges borders
Of equal importance?
Say you have everything perfect and qualify for a psa 10 except some whitening on the borders,ofc it depends on the amount but lets say 3 or 4 very minor whitening (ik that a 10 can have 2 micro dots but what happen if they are 4? ) does it go down to a 6 or do they have tolerance and is more likly to be a 8?
Also what if the surface is a 10 and the edges are more likly a 8 becouse of whitening? Again, are psa often tolerant or very strict?
Is the surface of bigger importance?
2.centering
Say again you have a sexy mint card but it doesnt qualify as a 7 bc of centering. Will you get a 6 (maybe even a 7, so the oc is ignored?!) or a 9 oc? Do you always get the 9 oc in these cases?
3.Is it even worth sending oc cards? I have a big amount clean mint cards that are a little off, i am rly struggling with this decision.
4.And this amazon tool to measure the center, is it any good? I hear, people even send the measurements in addition to the cards and get wrong measurements back (mybe coz of arrogance 
?)
5.upcharges: so if i understand correctly after 500$ value you pay 100$ per card right?
I have cards like pikachu base in 1st which might be a 10, so in germany its 400-500€ but there is no clear value.
Does psa base their value on ebay sales, are they even looking for value (many ppl told me they dont and its a gamble)?
Thanks if you even read this and even a bigger thanks if you can help me get a better overview !!