How many M&H BB's have you played? Is that particular M&H BB new or used (and how old if it's used)?
If ALL of them sound muddy to you (to you specifically, not any one else, since we all have different ears and have different threshold to qualify something as "muddy"), then it might be a fundamental characteristics of the M&H that you just do not like, (and may be too fundamental in the BB's tone for a tech to change). If that's the case, I'd say keep shopping.
If you have not played more than say, 2~3 M&H BB's, then there is a very good chance that the 4th, 5th, or 6th M&H BB you run into will have a bright enough bass to please you and you wouldn't have to compromise at all to buy that M&H BB.
Alternatively, you can make a request to the seller that he brighten up the bass further for your evaluation. Assuming the seller understand that you are very, very serious about the purchase and that the bass is your only stumbling block, a request like this may be well-received by the seller.
Good luck.