This is something i regularly struggle with as there’s multiple cards that i would like to upgrade but i very rarely get to do it as it usually feels there’s like more urgent things to buy. I usually buy straight the condition i’m comfortable with but buying from cardmarket sometimes leads into unpleasant surprises as often the sellers don’t add photos of the cards and i rely on their description and condition evaluation, but regardless of the condition if it’s not returned i often just place the card in its slot in binder and postpone its upgrading in distant future as i at least already have some sort of copy of the card
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Hey there,
If you prefer collecting M/NM cards, I would strongly recommend prioritizing those first instead of multiple damaged copies. Historically speaking, the better condition copies drive the price for that specific card.
The viral trade up challenge videos from recent years was my primary mantra decades ago when I had zero money to buy anything. Identifying what other collectors wanted, trading for their wants to leverage value into what you personally want without them realizing how much you want/need those cards, doing 3-way and occasionally even 4-way trades, sometimes intentionally taking two steps back with your collecting goals in order to position yourself with a better trade binder, are all things I did when I purely traded for my long term collecting goals. Incredibly time intensive but enjoyable as a collector 
Having been to recent trade shows, the time investment is still an effective approach to accomplishing a trade-only collection. Strategies have not changed significantly in recent years, only the $ value of individual cards
Hope this helps
cpbog1
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